Used this mod in conjunction with several others, and it never failed to crash at some point during a world. I tried with several different seeds and always crashed eventually. I picked one seed and found the crash spot, then started to removed mods until it no longer crashed. Not sure what exactly is causing it, but once this mod was removed and I went to the crash spot...no crash.
Quark Mod crash.txt

Upon restarting server without Quark as a mod, I'm getting an Unknown Structure Start: big_dungeon

As such, I think the creation of the big-dungeon may be causing the issue/crash.

forge-1.16.3-34.1.42-server.jar |Minecraft |minecraft |1.16.3
useful_backpacks-1.16.3-1.11.6.84.jar |Useful Backpacks |usefulbackpacks
DungeonsMod-1.16.3-1.1.1.jar |Dungeons Mod |dungeonsmod
randomloot-2.1.7.jar |Random Loot Mod |randomloot |2.1.7
BiomesOPlenty-1.16.3-12.0.0.416-universal.jar |Biomes O' Plenty |biomesoplenty
valhelsia_structures-16.0.5.jar |Valhelsia Structures |valhelsia_structures |16.0.5
pamhc2crops-1.16.3-1.0.1.jar |Pam's HarvestCraft 2 Crops |pamhc2crops
jei-1.16.3-7.6.0.49.jar |Just Enough Items |jei |7.5.0.43
simplefarming-1.16.3-1.3.5.jar |Simple Farming |simplefarming |1.16.3-1.3.5
DoggyTalents-1.16.3-2.0.1.0.jar |Doggy Talents 2 |doggytalents |2.0.1.0
curios-forge-1.16.3-4.0.2.0.jar |Curios API |curios |1.16.3-4.0.2.0
Botania-1.16.3-409.jar |Botania |botania |1.16.3-409
Patchouli-1.16.2-45.jar |Patchouli |patchouli |1.16.2-45
Xaeros_Minimap_20.27.2.1_Forge_1.16.4.jar |Xaero's Minimap |xaerominimap
pamhc2foodcore-1.16.3-1.0.0.jar |Pam's HarvestCraft 2 Food Core|pamhc2foodcore
XaerosWorldMap_1.11.0.1_Forge_1.16.4.jar |Xaero's World Map |xaeroworldmap
CookingForBlockheads_1.16.3-9.2.2.jar |Cooking for Blockheads |cookingforblockheads
Placebo-1.16.3-4.3.3.jar |Placebo |placebo |4.3.3
AutoRegLib-1.6-46.jar |AutoRegLib |autoreglib |1.6-46
ftb-gui-library-1603.1.1.25.jar |FTB GUI Library |ftbguilibrary |1603.1.1.25
DungeonCrawl-1.16.3-2.1.1.jar |Dungeon Crawl |dungeoncrawl |2.1.1
Bookshelf-1.16.3-8.7.20.jar |Bookshelf |bookshelf |8.7.20
u_team_core-1.16.3-3.1.12.185.jar |U Team Core |uteamcore |3.1.12.185
JustEnoughResources-1.16.3-0.12.0.102.jar |Just Enough Resources |jeresources |0.12.0.102
ftb-chunks-1603.2.0.42.jar |FTB Chunks |ftbchunks |1603.2.0.42
forge-1.16.3-34.1.42-universal.jar |Forge |forge |34.1.42
Aquaculture-1.16.3-2.1.5.jar |Aquaculture 2 |aquaculture |1.16.3-2.1.5
scuba-gear-1.16.3-1.0.1.jar |Scuba Gear |scuba_gear |1.0.1
FastLeafDecay-v25.jar |FastLeafDecay |fastleafdecay |v25
ironchest-1.16.3-11.2.6.jar |Iron Chests |ironchest |1.16.3-11.2.6

Plus yours: Quark - r2.4-271.jar

Also to note: the first 2 mods I deleted and tested without were; DungeonsMod & DungeonCrawl. It still crashed without those two.

Also getting crashes on launch with Quark-r2.4-275

Crashes with exit code 0 when pressing Play in launcher.

Other mods:
collective-1.16.4-1.53
doubledoors_1.16.4-2.1
guiclock_1.16.4-2.0
guicompass_1.16.4-1.3
guifollowers_1.16.4-1.0
healingcf_1.16.4-3.1
mineralchance_1.16.4-1.0
MorePaths-1.16.4-1.0
nametagtweeks_1.16.4-1.2
nhacampfire_1.16.4-3.0
nutritiousmilk_1.16.4-1.2
petnames1.16.4-1.2
quickpaths_1.16.4-1.2
replantingcrops_1.16.4-1.2
scaffoldingdropsnearby_1.16.4-1.1
spidersprwebs_1.16.4-1.0.1
stackrefill_1.16.4-1.1
storage_overhaul-1.16.4-1.0.1
wooltweaks_1.16.4-1.0

Also some resourcepacks and datapacks from vanilla tweaks.

Adding Quark to mods causes crash from launcher.
Removed all mods, resourcepacks, and datapacks.
Relaunched game with only:
forge-1.16.4-35.0.7-client
forge-1.16.4-35.0.7-universal
Opened world successfully.
Added only Quark.
Game crashed from launcher.
Removed Quark.
Relaunched game with only forge client and universal.
Opened world successfully.
Ran several testing cycles with all mods except Quark or Quark only with no mod launches in between.
Same results each time (Quark crashes, everything else okay) except after fourth cycle with Quark only game crashed attempting to open launcher. Had to restart computer to restore Minecraft functionality.

Thank you for your attention and all your hard work keeping us entertained making a great game better.

I'm having this same problem and I've recently had my previous world that I used to play on that apon loading into it that it crashed and is now unloadable/un-joinable due to Quark and how I know that the problem is from Quark is that in the crash report at the first line it has the mod name quark;

java.lang.NullPointerException: mouseClicked event handler
at vazkii.quark.base.world.WorldGenHandler.onBiomesLoaded(WorldGenHandler.java:70) ~[quark:r2.4-275] {re:classloading}
(This is from my latest crash report btw)

Also right now I'm in the process of making a brand new modded world and in the datapacks section it says that quarks datapack is:

Incompatible
(Made for older version of Minecraft)

So there's something wrong with Quarks datapacks apparently...

P.S. I deleted the world I used to play on up till the crash and that's why I'm in the process of making a new modded world even tho I could've simply removed Quark but might've caused some miner or major issues to the world and worldgen if I removed Quark and my new modded world won't have Quark till this issue with Quark and its datapacks gets fixed. Btw Quark is an amazing mod and on my last modded world before I deleted it I had found a massive lava lake or it could've been a lava ocean in the overworld (I was looking at it in creative mode not survival mode btw). Keep up the great work!

with the latest Quark i see this error and game wont load
[09:46:23] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1061]: Caused by: java.lang.IllegalArgumentException: The specified resource 'quark.mixins.json' was invalid or could not be read

All these crashes look unrelated to each other.

I'm going to be closing this one due to all the different crashes people have reported here. The OP is also reflected on #2663, which is cleaner, so I'll be having a look at that one.

As for the mixin crash, @gotchanhonmono, if you can give it another try using all the latest versions of forge, quark, and ARL, that'd be appreciated. If it still happens please open a new issue.