I got this error from a capuchin monkey in someone's chunk-loaded base. It didn't happen immediately though, so I was able to remove the monkey with commands, and that solved the issue. I think the monkey was on a lead too.

net.minecraft.crash.ReportedException: Ticking entity
        at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:855) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:A,pl:runtimedistcleaner:A}
        at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:291) ~[?:?] {re:classloading,pl:accesstransformer:B}
        at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:787) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:A,pl:runtimedistcleaner:A}
        at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:642) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:A,pl:runtimedistcleaner:A}
        at net.minecraft.server.MinecraftServer.func_240783_a_(MinecraftServer.java:232) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:A,pl:runtimedistcleaner:A}
        at java.lang.Thread.run(Thread.java:748) [?:1.8.0_282] {}
Caused by: java.lang.NullPointerException
        at net.minecraft.pathfinding.PathNavigator.func_75487_m(PathNavigator.java:304) ~[?:?] {re:mixin,re:classloading,pl:mixin:APP:performant.mixins.json:pathing.PathNavigatorMixin,pl:mixin:A}
        at net.minecraft.pathfinding.GroundPathNavigator.func_75487_m(SourceFile:97) ~[?:?] {re:mixin,re:classloading,pl:mixin:APP:performant.mixins.json:pathing.GroundPathNavigatorMixin,pl:mixin:A}
        at net.minecraft.pathfinding.PathNavigator.func_75484_a(PathNavigator.java:162) ~[?:?] {re:mixin,re:classloading,pl:mixin:APP:performant.mixins.json:pathing.PathNavigatorMixin,pl:mixin:A}
        at net.minecraft.pathfinding.PathNavigator.func_75492_a(PathNavigator.java:142) ~[?:?] {re:mixin,re:classloading,pl:mixin:APP:performant.mixins.json:pathing.PathNavigatorMixin,pl:mixin:A}
        at net.minecraft.entity.CreatureEntity.func_110159_bB(SourceFile:572) ~[?:?] {re:mixin,re:classloading,pl:mixin:APP:performant.mixins.json:entity.CreatureEntityMixin,pl:mixin:A}
        at net.minecraft.entity.MobEntity.func_70071_h_(MobEntity.java:302) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:assets/botania/botania.mixins.json:AccessorMobEntity,pl:mixin:APP:performant.mixins.json:entity.MobEntityMixin,pl:mixin:A,pl:runtimedistcleaner:A}
        at com.github.alexthe666.alexsmobs.entity.EntityCapuchinMonkey.func_70071_h_(EntityCapuchinMonkey.java:172) ~[alexsmobs:1.10.0] {re:classloading}
        at net.minecraft.world.server.ServerWorld.func_217479_a(ServerWorld.java:611) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:world.ServerWorldBlockUpdateMixin,pl:mixin:APP:immersiveengineering.mixins.json:coremods.ServerWorldMixin,pl:mixin:APP:quark.mixins.json:ServerWorldMixin,pl:mixin:APP:performant.mixins.json:world.ServerWorldMixin,pl:mixin:APP:performant.mixins.json:entity.MobServerWorldMixin,pl:mixin:A,pl:runtimedistcleaner:A}
        at net.minecraft.world.World.func_217390_a(World.java:554) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,xf:fml:observerlib:coremodmethod,xf:fml:astralsorcery:sun_brightness_server,pl:mixin:APP:performant.mixins.json:world.WorldMixin,pl:mixin:A,pl:runtimedistcleaner:A}
        at net.minecraft.world.server.ServerWorld.func_72835_b(ServerWorld.java:404) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:world.ServerWorldBlockUpdateMixin,pl:mixin:APP:immersiveengineering.mixins.json:coremods.ServerWorldMixin,pl:mixin:APP:quark.mixins.json:ServerWorldMixin,pl:mixin:APP:performant.mixins.json:world.ServerWorldMixin,pl:mixin:APP:performant.mixins.json:entity.MobServerWorldMixin,pl:mixin:A,pl:runtimedistcleaner:A}
        at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:851) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:A,pl:runtimedistcleaner:A}
        ... 5 more

bug caused by preformant. remove this mod or ask their devs to fix this ancient bug.

Having this issue as well. There is a monkey on a leash that crashes the server at random points.

Time: 7/14/21, 3:57 AM
Description: Ticking entity

java.lang.NullPointerException: Ticking entity
at net.minecraft.pathfinding.PathNavigator.func_75484_a(PathNavigator.java:185) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:pathing.PathNavigatorMixin,pl:mixin:A}
at net.minecraft.pathfinding.PathNavigator.func_75492_a(PathNavigator.java:143) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:pathing.PathNavigatorMixin,pl:mixin:A}
at net.minecraft.entity.CreatureEntity.func_110159_bB(CreatureEntity.java:572) ~[?:?] {re:mixin,re:classloading,pl:mixin:APP:performant.mixins.json:entity.CreatureEntityMixin,pl:mixin:A}
at net.minecraft.entity.MobEntity.func_70071_h_(MobEntity.java:341) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:the_bumblezone.mixins.json:items.HoneyShieldCooldownMixin,pl:mixin:APP:the_bumblezone.mixins.json:items.HoneyShieldPreferredSlotMixin,pl:mixin:APP:charm.mixins.json:accessor.MobEntityAccessor,pl:mixin:APP:buzzier_bees.mixins.json:MobEntityMixin,pl:mixin:APP:assets/botania/botania.mixins.json:AccessorMobEntity,pl:mixin:APP:performant.mixins.json:entity.MobEntityDespawnMixin,pl:mixin:APP:performant.mixins.json:entity.MobEntityMixin,pl:mixin:A,pl:runtimedistcleaner:A}
at com.github.alexthe666.alexsmobs.entity.EntityCapuchinMonkey.func_70071_h_(EntityCapuchinMonkey.java:172) ~[alexsmobs:1.11.1] {re:classloading}
at net.minecraft.world.server.ServerWorld.func_217479_a(ServerWorld.java:952) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:world.ServerWorldBlockUpdateMixin,pl:mixin:APP:the_bumblezone.mixins.json:world.ServerWorldMixin,pl:mixin:APP:charm.mixins.json:ServerWorldMixin,pl:mixin:APP:charm.mixins.json:accessor.ServerWorldAccessor,pl:mixin:APP:abnormals_core.mixins.json:ServerWorldMixin,pl:mixin:APP:quark.mixins.json:ServerWorldMixin,pl:mixin:APP:performant.mixins.json:world.ServerWorldMixin,pl:mixin:APP:performant.mixins.json:entity.MobServerWorldMixin,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.world.World.func_217390_a(World.java:794) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,xf:fml:twilightforest:hitbox,pl:mixin:APP:sereneseasons.mixins.json:MixinWorld,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.world.server.ServerWorld.func_72835_b(ServerWorld.java:696) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:world.ServerWorldBlockUpdateMixin,pl:mixin:APP:the_bumblezone.mixins.json:world.ServerWorldMixin,pl:mixin:APP:charm.mixins.json:ServerWorldMixin,pl:mixin:APP:charm.mixins.json:accessor.ServerWorldAccessor,pl:mixin:APP:abnormals_core.mixins.json:ServerWorldMixin,pl:mixin:APP:quark.mixins.json:ServerWorldMixin,pl:mixin:APP:performant.mixins.json:world.ServerWorldMixin,pl:mixin:APP:performant.mixins.json:entity.MobServerWorldMixin,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:1061) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:charm.mixins.json:accessor.MinecraftServerAccessor,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:333) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:965) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:charm.mixins.json:accessor.MinecraftServerAccessor,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:778) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:charm.mixins.json:accessor.MinecraftServerAccessor,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.server.MinecraftServer.func_240783_a_(MinecraftServer.java:283) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:charm.mixins.json:accessor.MinecraftServerAccessor,pl:mixin:A,pl:runtimedistcleaner:A}
at java.lang.Thread.run(Thread.java:829) [?:?] {}

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

-- Head --
Thread: Server thread
Stacktrace:
at net.minecraft.pathfinding.PathNavigator.func_75484_a(PathNavigator.java:185) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:pathing.PathNavigatorMixin,pl:mixin:A}
at net.minecraft.pathfinding.PathNavigator.func_75492_a(PathNavigator.java:143) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:pathing.PathNavigatorMixin,pl:mixin:A}
at net.minecraft.entity.CreatureEntity.func_110159_bB(CreatureEntity.java:572) ~[?:?] {re:mixin,re:classloading,pl:mixin:APP:performant.mixins.json:entity.CreatureEntityMixin,pl:mixin:A}
at net.minecraft.entity.MobEntity.func_70071_h_(MobEntity.java:341) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:the_bumblezone.mixins.json:items.HoneyShieldCooldownMixin,pl:mixin:APP:the_bumblezone.mixins.json:items.HoneyShieldPreferredSlotMixin,pl:mixin:APP:charm.mixins.json:accessor.MobEntityAccessor,pl:mixin:APP:buzzier_bees.mixins.json:MobEntityMixin,pl:mixin:APP:assets/botania/botania.mixins.json:AccessorMobEntity,pl:mixin:APP:performant.mixins.json:entity.MobEntityDespawnMixin,pl:mixin:APP:performant.mixins.json:entity.MobEntityMixin,pl:mixin:A,pl:runtimedistcleaner:A}
at com.github.alexthe666.alexsmobs.entity.EntityCapuchinMonkey.func_70071_h_(EntityCapuchinMonkey.java:172) ~[alexsmobs:1.11.1] {re:classloading}
at net.minecraft.world.server.ServerWorld.func_217479_a(ServerWorld.java:952) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:world.ServerWorldBlockUpdateMixin,pl:mixin:APP:the_bumblezone.mixins.json:world.ServerWorldMixin,pl:mixin:APP:charm.mixins.json:ServerWorldMixin,pl:mixin:APP:charm.mixins.json:accessor.ServerWorldAccessor,pl:mixin:APP:abnormals_core.mixins.json:ServerWorldMixin,pl:mixin:APP:quark.mixins.json:ServerWorldMixin,pl:mixin:APP:performant.mixins.json:world.ServerWorldMixin,pl:mixin:APP:performant.mixins.json:entity.MobServerWorldMixin,pl:mixin:A,pl:runtimedistcleaner:A}
-- Entity being ticked --
Details:
Entity Type: alexsmobs:capuchin_monkey (com.github.alexthe666.alexsmobs.entity.EntityCapuchinMonkey)
Entity ID: 34981
Entity Name: Capuchin Monkey
Entity's Exact location: 4241.42, 67.00, 3377.82
Entity's Block location: World: (4241,67,3377), Chunk: (at 1,4,1 in 265,211; contains blocks 4240,0,3376 to 4255,255,3391), Region: (8,6; contains chunks 256,192 to 287,223, blocks 4096,0,3072 to 4607,255,3583)
Entity's Momentum: 0.00, -0.08, 0.00
Entity's Passengers: []
Entity's Vehicle: ERROR NullPointerException: null
Stacktrace:
at net.minecraft.world.World.func_217390_a(World.java:794) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,xf:fml:twilightforest:hitbox,pl:mixin:APP:sereneseasons.mixins.json:MixinWorld,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.world.server.ServerWorld.func_72835_b(ServerWorld.java:696) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:performant.mixins.json:world.ServerWorldBlockUpdateMixin,pl:mixin:APP:the_bumblezone.mixins.json:world.ServerWorldMixin,pl:mixin:APP:charm.mixins.json:ServerWorldMixin,pl:mixin:APP:charm.mixins.json:accessor.ServerWorldAccessor,pl:mixin:APP:abnormals_core.mixins.json:ServerWorldMixin,pl:mixin:APP:quark.mixins.json:ServerWorldMixin,pl:mixin:APP:performant.mixins.json:world.ServerWorldMixin,pl:mixin:APP:performant.mixins.json:entity.MobServerWorldMixin,pl:mixin:A,pl:runtimedistcleaner:A}