-- Head --
Thread: Client thread
Stacktrace:
at net.minecraft.entity.item.EntityBoat.func_70271_g(EntityBoat.java:864)
at net.minecraft.client.renderer.entity.RenderBoat.func_188311_a(SourceFile:52)
at net.minecraft.client.renderer.entity.RenderBoat.func_76986_a(SourceFile:32)
at net.minecraft.client.renderer.entity.RenderBoat.func_76986_a(SourceFile:11)

-- Entity being rendered --
Details:
Entity Type: minecraft:boat (net.minecraft.entity.item.EntityBoat)
Entity ID: 836
Entity Name: Boat
Entity's Exact location: 211.86, 62.88, 259.66
Entity's Block location: World: (211,62,259), Chunk: (at 3,3,3 in 13,16; contains blocks 208,0,256 to 223,255,271), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Entity's Momentum: 0.00, 0.00, 0.00
Entity's Passengers: []
Entity's Vehicle: ERROR NullPointerException: null

-- Renderer details --
Details:
Assigned renderer: net.minecraft.client.renderer.entity.RenderBoat@440eab36
Location: -0.47,0.28,-2.00 - World: (-1,0,-3), Chunk: (at 15,0,13 in -1,-1; contains blocks -16,0,-16 to -1,255,-1), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Rotation: 119.47848
Delta: 0.72002095
Stacktrace:
at net.minecraft.client.renderer.entity.RenderManager.func_188391_a(RenderManager.java:384)
at net.minecraft.client.renderer.entity.RenderManager.func_188388_a(RenderManager.java:368)
at net.minecraft.client.renderer.RenderGlobal.func_180446_a(RenderGlobal.java:628)
at net.minecraft.client.renderer.EntityRenderer.func_175068_a(EntityRenderer.java:1347)
at net.minecraft.client.renderer.EntityRenderer.func_78471_a(EntityRenderer.java:1259)

I get this any time someone tries to place a boat on my server. It will then not let anyone back into the server without crashing their client. I know it's quark because I can run any mod just fine, but as soon as I introduce quark into the mix, it messes up. Even if Quark is the only mod on the server.

Any help would be appreciated.

No one has any helpful advice to this? I can't imagine that everyone is just dealing with it.

For additional information:
Server is running Forge 1.12.2-14.23.4.2705
Even with Quark and AutoRegLib as the only mods on the server, it will still have this problem. New world and everything.

AutoRegLib-1.3-18 (have also tried several older versions)
Quark-r1.4-125 (have also tried several older versions)

Can you get a full log of the entire crash that happens to someone after they try to log in?

---- Minecraft Crash Report ----

WARNING: coremods are present:
LoadingPlugin (Quark-r1.4-125.jar)
Contact their authors BEFORE contacting forge

// Quite honestly, I wouldn't worry myself about that.

Time: 8/6/18 6:12 PM
Description: Rendering entity in world

java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Float
at net.minecraft.entity.item.EntityBoat.func_70271_g(EntityBoat.java:864)
at net.minecraft.client.renderer.entity.RenderBoat.func_188311_a(SourceFile:52)
at net.minecraft.client.renderer.entity.RenderBoat.func_76986_a(SourceFile:32)
at net.minecraft.client.renderer.entity.RenderBoat.func_76986_a(SourceFile:11)
at net.minecraft.client.renderer.entity.RenderManager.func_188391_a(RenderManager.java:384)
at net.minecraft.client.renderer.entity.RenderManager.func_188388_a(RenderManager.java:368)
at net.minecraft.client.renderer.RenderGlobal.func_180446_a(RenderGlobal.java:628)
at net.minecraft.client.renderer.EntityRenderer.func_175068_a(EntityRenderer.java:1345)
at net.minecraft.client.renderer.EntityRenderer.func_78471_a(EntityRenderer.java:1259)
at net.minecraft.client.renderer.EntityRenderer.func_181560_a(EntityRenderer.java:1062)
at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1117)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:397)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

A detailed walkthrough of the error, its code path and all known details is as follows:

-- Head --
Thread: Client thread
Stacktrace:
at net.minecraft.entity.item.EntityBoat.func_70271_g(EntityBoat.java:864)
at net.minecraft.client.renderer.entity.RenderBoat.func_188311_a(SourceFile:52)
at net.minecraft.client.renderer.entity.RenderBoat.func_76986_a(SourceFile:32)
at net.minecraft.client.renderer.entity.RenderBoat.func_76986_a(SourceFile:11)

-- Entity being rendered --
Details:
Entity Type: minecraft:boat (net.minecraft.entity.item.EntityBoat)
Entity ID: 3104
Entity Name: Boat
Entity's Exact location: 124.77, 62.88, 167.44
Entity's Block location: World: (124,62,167), Chunk: (at 12,3,7 in 7,10; contains blocks 112,0,160 to 127,255,175), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Entity's Momentum: 0.00, 0.00, 0.00
Entity's Passengers: []
Entity's Vehicle: ERROR NullPointerException: null

-- Renderer details --
Details:
Assigned renderer: net.minecraft.client.renderer.entity.RenderBoat@d37d9eb
Location: -1.42,-0.12,0.62 - World: (-2,-1,0), Chunk: (at 14,-1,0 in -1,0; contains blocks -16,0,0 to -1,255,15), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Rotation: 24.580893
Delta: 0.37999448
Stacktrace:
at net.minecraft.client.renderer.entity.RenderManager.func_188391_a(RenderManager.java:384)
at net.minecraft.client.renderer.entity.RenderManager.func_188388_a(RenderManager.java:368)
at net.minecraft.client.renderer.RenderGlobal.func_180446_a(RenderGlobal.java:628)
at net.minecraft.client.renderer.EntityRenderer.func_175068_a(EntityRenderer.java:1345)
at net.minecraft.client.renderer.EntityRenderer.func_78471_a(EntityRenderer.java:1259)

-- Affected level --
Details:
Level name: MpServer
All players: 1 total; [EntityPlayerSP['PlayerName'/1846, l='MpServer', x=126.18, y=63.00, z=166.82]]
Chunk stats: MultiplayerChunkCache: 289, 289
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: World: (136,64,168), Chunk: (at 8,4,8 in 8,10; contains blocks 128,0,160 to 143,255,175), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 6022 game time, 6022 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Forced entities: 84 total; [EntityPlayerSP['PlayerName'/1846, l='MpServer', x=126.18, y=63.00, z=166.82], EntityZombie['Zombie'/2304, l='MpServer', x=75.50, y=38.00, z=217.50], EntitySkeleton['Skeleton'/2567, l='MpServer', x=119.29, y=25.00, z=122.49], EntityBat['Bat'/2057, l='MpServer', x=147.25, y=20.36, z=104.75], EntityCreeper['Creeper'/2569, l='MpServer', x=119.20, y=32.00, z=121.56], EntityBat['Bat'/2058, l='MpServer', x=150.62, y=20.00, z=102.70], EntityZombie['Zombie'/2445, l='MpServer', x=183.24, y=20.00, z=142.50], EntityZombie['Zombie'/2446, l='MpServer', x=166.50, y=14.00, z=142.50], EntityZombie['Zombie'/2447, l='MpServer', x=167.50, y=14.00, z=146.50], EntityCreeper['Creeper'/2831, l='MpServer', x=97.50, y=33.00, z=193.50], EntityCreeper['Creeper'/2065, l='MpServer', x=126.22, y=31.00, z=117.48], EntityBat['Bat'/2961, l='MpServer', x=64.58, y=30.87, z=203.51], EntityBat['Bat'/2962, l='MpServer', x=64.41, y=30.04, z=205.69], EntityBat['Bat'/2963, l='MpServer', x=63.49, y=31.10, z=202.63], EntityZombie['Zombie'/2452, l='MpServer', x=190.50, y=20.00, z=134.50], EntitySkeleton['Skeleton'/1943, l='MpServer', x=82.50, y=15.00, z=240.50], EntitySkeleton['Skeleton'/2456, l='MpServer', x=95.29, y=37.00, z=146.49], EntityBoat['Boat'/3104, l='MpServer', x=124.77, y=62.88, z=167.44], EntityAshen['Ashen'/2469, l='MpServer', x=120.29, y=15.00, z=132.48], EntityZombie['Zombie'/2726, l='MpServer', x=124.14, y=18.00, z=125.19], EntityZombie['Zombie'/2727, l='MpServer', x=134.50, y=22.00, z=116.50], EntityChicken['Chicken'/53, l='MpServer', x=97.37, y=78.00, z=96.47], EntityChicken['Chicken'/54, l='MpServer', x=96.50, y=78.00, z=97.50], EntityChicken['Chicken'/55, l='MpServer', x=96.71, y=78.00, z=98.18], EntityCreeper['Creeper'/1847, l='MpServer', x=100.50, y=31.00, z=210.50], EntityBat['Bat'/2231, l='MpServer', x=125.59, y=19.96, z=122.37], EntityChicken['Chicken'/56, l='MpServer', x=97.50, y=78.00, z=93.50], EntityZombie['Zombie'/2105, l='MpServer', x=144.50, y=33.00, z=88.50], EntitySkeleton['Skeleton'/2620, l='MpServer', x=206.50, y=30.00, z=139.50], EntityCreeper['Creeper'/2878, l='MpServer', x=97.50, y=20.00, z=138.50], EntityBat['Bat'/1860, l='MpServer', x=136.45, y=32.10, z=101.25], EntitySquid['Squid'/1862, l='MpServer', x=93.45, y=60.00, z=162.60], EntitySquid['Squid'/1863, l='MpServer', x=64.78, y=61.93, z=189.62], EntityZombie['Zombie'/2760, l='MpServer', x=103.50, y=25.00, z=125.50], EntityCow['Cow'/81, l='MpServer', x=147.50, y=71.00, z=104.50], EntityCow['Cow'/82, l='MpServer', x=147.50, y=71.00, z=104.50], EntityCow['Cow'/83, l='MpServer', x=147.50, y=71.00, z=105.50], EntityCow['Cow'/84, l='MpServer', x=147.50, y=71.00, z=106.50], EntityZombie['Zombie'/2516, l='MpServer', x=81.48, y=36.00, z=125.28], EntityCow['Cow'/85, l='MpServer', x=138.49, y=69.00, z=140.23], EntityZombie['Zombie'/2005, l='MpServer', x=168.50, y=14.00, z=143.50], EntityCow['Cow'/86, l='MpServer', x=140.50, y=69.00, z=135.50], EntityZombie['Zombie'/2006, l='MpServer', x=166.50, y=14.00, z=143.50], EntityBat['Bat'/2262, l='MpServer', x=156.55, y=19.02, z=108.20], EntityCow['Cow'/87, l='MpServer', x=133.80, y=68.00, z=141.52], EntityCow['Cow'/88, l='MpServer', x=138.50, y=68.00, z=132.50], EntityCreeper['Creeper'/2648, l='MpServer', x=107.10, y=29.00, z=138.50], EntityPig['Pig'/89, l='MpServer', x=144.50, y=64.00, z=221.60], EntityCreeper['Creeper'/2137, l='MpServer', x=94.86, y=39.00, z=159.43], EntityPig['Pig'/90, l='MpServer', x=146.46, y=67.00, z=222.76], EntityPig['Pig'/91, l='MpServer', x=147.50, y=71.00, z=227.50], EntityPig['Pig'/92, l='MpServer', x=143.41, y=63.00, z=227.25], EntityZombie['Zombie'/2780, l='MpServer', x=167.50, y=14.00, z=140.50], EntityPig['Pig'/93, l='MpServer', x=151.49, y=73.00, z=171.78], EntityPig['Pig'/94, l='MpServer', x=160.55, y=79.00, z=170.45], EntityZombie['Zombie'/2782, l='MpServer', x=177.22, y=16.00, z=139.50], EntityPig['Pig'/95, l='MpServer', x=162.82, y=74.00, z=179.57], EntityZombie['Zombie'/2783, l='MpServer', x=171.70, y=14.00, z=143.60], EntityPig['Pig'/96, l='MpServer', x=157.62, y=70.00, z=185.23], EntitySpider['Spider'/2529, l='MpServer', x=134.50, y=32.00, z=98.50], EntityCreeper['Creeper'/2788, l='MpServer', x=140.50, y=26.00, z=102.50], EntitySkeleton['Skeleton'/2789, l='MpServer', x=139.50, y=26.00, z=99.50], EntitySkeleton['Skeleton'/2790, l='MpServer', x=139.50, y=26.00, z=101.50], EntityBat['Bat'/2281, l='MpServer', x=109.25, y=37.10, z=148.41], EntityZombie['Zombie'/2538, l='MpServer', x=189.50, y=20.00, z=178.50], EntityCreeper['Creeper'/2411, l='MpServer', x=123.50, y=23.00, z=120.50], EntityZombie['Zombie'/2539, l='MpServer', x=190.50, y=20.00, z=178.50], EntityPig['Pig'/109, l='MpServer', x=193.50, y=77.00, z=217.50], EntitySpider['Spider'/2029, l='MpServer', x=99.50, y=32.00, z=212.50], EntityPig['Pig'/110, l='MpServer', x=194.50, y=76.00, z=220.50], EntitySquid['Squid'/1902, l='MpServer', x=100.26, y=56.31, z=180.29], EntityPig['Pig'/111, l='MpServer', x=195.50, y=76.00, z=221.50], EntitySquid['Squid'/1903, l='MpServer', x=109.10, y=62.55, z=202.39], EntityPig['Pig'/112, l='MpServer', x=195.50, y=76.00, z=221.50], EntitySquid['Squid'/1904, l='MpServer', x=108.40, y=57.53, z=195.62], EntityZombie['Zombie'/2544, l='MpServer', x=200.50, y=31.00, z=150.50], EntityZombie['Zombie'/2545, l='MpServer', x=196.50, y=31.00, z=151.50], EntityPig['Pig'/117, l='MpServer', x=203.50, y=64.00, z=103.50], EntityBat['Bat'/2934, l='MpServer', x=99.64, y=16.04, z=129.06], EntityPig['Pig'/119, l='MpServer', x=203.50, y=64.00, z=103.50], EntityZombie['Zombie'/2167, l='MpServer', x=100.50, y=30.00, z=135.50], EntityBat['Bat'/2935, l='MpServer', x=97.20, y=14.11, z=130.50], EntityPig['Pig'/120, l='MpServer', x=204.50, y=70.00, z=100.50], EntitySkeleton['Skeleton'/2303, l='MpServer', x=77.70, y=38.00, z=222.70]]
Retry entities: 0 total; []
Server brand: fml,forge
Server type: Non-integrated multiplayer server
Stacktrace:
at net.minecraft.client.multiplayer.WorldClient.func_72914_a(WorldClient.java:420)
at net.minecraft.client.Minecraft.func_71396_d(Minecraft.java:2738)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:418)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

-- System Details --
Details:
Minecraft Version: 1.12.2
Operating System: Windows 10 (amd64) version 10.0
Java Version: 1.8.0_181, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 3939850896 bytes (3757 MB) / 4294967296 bytes (4096 MB) up to 4294967296 bytes (4096 MB)
JVM Flags: 5 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xms4096m -Xmx4096m -XX:+UseG1GC -XX:MaxGCPauseMillis=4
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
FML: MCP 9.42 Powered by Forge 14.23.4.2705 6 mods loaded, 6 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored

State	ID	Version	Source	Signature
UCHIJA	minecraft	1.12.2	minecraft.jar	None
UCHIJA	mcp	9.42	minecraft.jar	None
UCHIJA	FML	8.0.99.99	modpack.jar	e3c3d50c7c986df74c645c0ac54639741c90a557
UCHIJA	forge	14.23.4.2705	modpack.jar	e3c3d50c7c986df74c645c0ac54639741c90a557
UCHIJA	quark	r1.4-125	Quark-r1.4-125.jar	None
UCHIJA	autoreglib	1.3-18	AutoRegLib-1.3-18.jar	None

Loaded coremods (and transformers):
LoadingPlugin (Quark-r1.4-125.jar)
vazkii.quark.base.asm.ClassTransformer
GL info: ' Vendor: 'NVIDIA Corporation' Version: '4.6.0 NVIDIA 398.82' Renderer: 'GeForce GTX 970/PCIe/SSE2'
Launched Version: 1.12.2-forge1.12.2-14.23.4.2705
LWJGL: 2.9.4
OpenGL: GeForce GTX 970/PCIe/SSE2 GL version 4.6.0 NVIDIA 398.82, NVIDIA Corporation
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: Yes
Is Modded: Definitely; Client brand changed to 'fml,forge'
Type: Client (map_client.txt)
Resource Packs:
Current Language: English (US)
Profiler Position: N/A (disabled)
CPU: 8x AMD Ryzen 5 1500X Quad-Core Processor

Let me know if you need anything else.

Turns out that it was the server host that I was using. I was already fighting them on how my server was getting terrible overload on the CPU, so I ported my server over to another host and found that the server ran way better. Not only did it run smoother without overload on the CPU, but the issue of the boats went away. Can't explain why it only did it while quark was on the server, but it appears to be fine with quark on this other server.