[06:04:43] [Server thread/WARN] [minecraft/EntityDataManager]: defineId called for: class its_meow.betteranimalsplus.common.entity.EntityLamprey from class dev.itsmeow.betteranimalsplus.imdlib.entity.util.EntityTypeContainer
[06:04:43] [Server thread/WARN] [minecraft/EntityDataManager]: defineId called for: class its_meow.betteranimalsplus.common.entity.EntityLamprey from class its_meow.betteranimalsplus.common.entity.util.EntityTypeContainerBAP
[06:04:48] [Server thread/ERROR] [minecraft/Structures]: Unknown structure piece id: minecraft:bigdungeon
[06:04:48] [Server thread/ERROR] [minecraft/Structures]: Unknown structure piece id: minecraft:bigdungeon
[06:04:48] [Server thread/ERROR] [minecraft/Structures]: Unknown structure piece id: minecraft:bigdungeon
[06:04:48] [Server thread/ERROR] [minecraft/Structures]: Unknown structure piece id: minecraft:bigdungeon
[06:04:48] [Server thread/ERROR] [minecraft/Structures]: Unknown structure piece id: minecraft:bigdungeon
[06:04:50] [Server thread/ERROR] [minecraft/MinecraftServer]: Encountered an unexpected exception
java.util.concurrent.CompletionException: net.minecraft.crash.ReportedException: Exception generating new chunk
at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273) ~[?:1.8.0_252] {}
at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280) ~[?:1.8.0_252] {}
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:975) ~[?:1.8.0_252] {}
at java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:940) ~[?:1.8.0_252] {}
at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:456) ~[?:1.8.0_252] {}
at net.minecraft.world.chunk.ChunkTaskPriorityQueueSorter.func_219083_b(SourceFile:58) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.func_213148_e(SourceFile:83) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.func_213145_a(SourceFile:123) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.run(SourceFile:91) ~[?:?] {re:classloading}
at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402) ~[?:1.8.0_252] {}
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289) ~[?:1.8.0_252] {}
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056) ~[?:1.8.0_252] {}
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692) ~[?:1.8.0_252] {}
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157) ~[?:1.8.0_252] {}
Caused by: net.minecraft.crash.ReportedException: Exception generating new chunk
at net.minecraft.world.server.ChunkManager.lambda$null$18(ChunkManager.java:529) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at com.mojang.datafixers.util.Either$Left.map(Either.java:38) ~[?:?] {re:classloading}
at net.minecraft.world.server.ChunkManager.lambda$func_223156_b$20(ChunkManager.java:516) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:966) ~[?:1.8.0_252] {}
... 11 more
Caused by: java.lang.NullPointerException
at net.minecraft.nbt.StringNBT.func_229705_a_(StringNBT.java:40) ~[?:?] {re:classloading}
at net.minecraft.nbt.CompoundNBT.func_74778_a(CompoundNBT.java:145) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:fml:randompatches:RandomPatches CompoundNBT Transformer,re:mixin,pl:accesstransformer:B}
at dev.itsmeow.betteranimalsplus.imdlib.entity.util.IVariantTypes.writeType(IVariantTypes.java:41) ~[?:9.0.1] {re:classloading}
at its_meow.betteranimalsplus.common.entity.util.abstracts.EntityAnimalWithTypes.func_184198_c(EntityAnimalWithTypes.java:30) ~[?:9.0.1] {re:classloading}
at net.minecraft.entity.Entity.func_70039_c(Entity.java:1309) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,xf:fml:quark:generic-update-hook,xf:fml:quark:override-collision,xf:fml:immersiveengineering:IE wire damage,xf:fml:randompatches:RandomPatches Entity Transformer,xf:fml:midnight:LadderNoises,pl:runtimedistcleaner:A}
at net.minecraft.world.chunk.ChunkPrimer.func_76612_a(ChunkPrimer.java:213) ~[?:?] {re:classloading}
at net.minecraft.world.gen.WorldGenRegion.func_217376_c(WorldGenRegion.java:250) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
at net.minecraft.world.spawner.WorldEntitySpawner.func_77191_a(WorldEntitySpawner.java:264) ~[?:?] {re:mixin,re:classloading}
at net.minecraft.world.gen.OverworldChunkGenerator.func_202093_c(SourceFile:56) ~[?:?] {re:classloading}
at net.minecraft.world.chunk.ChunkStatus.lambda$static$12(ChunkStatus.java:86) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.chunk.ChunkStatus$ISelectiveWorker.doWork(ChunkStatus.java:237) ~[?:?] {re:classloading}
at net.minecraft.world.chunk.ChunkStatus.func_223198_a(ChunkStatus.java:195) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.server.ChunkManager.lambda$null$18(ChunkManager.java:518) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at com.mojang.datafixers.util.Either$Left.map(Either.java:38) ~[?:?] {re:classloading}(B
at net.minecraft.world.server.ChunkManager.lambda$func_223156_b$20(ChunkManager.java:516) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:966) ~[?:1.8.0_252] {}
... 11 more
[06:04:50] [Server thread/ERROR] [minecraft/MinecraftServer]: This crash report has been saved to: /opt/service/./crash-reports/crash-2020-08-11_06.04.50-server.txt
[06:04:50] [Server thread/INFO] [minecraft/MinecraftServer]: Stopping server
[06:04:50] [Server thread/INFO] [minecraft/MinecraftServer]: Saving players
[06:04:50] [Server thread/INFO] [minecraft/ServerPlayNetHandler]: SpMino lost connection: Internal Exception: java.lang.StackOverflowError
[06:04:50] [Server thread/INFO] [minecraft/DedicatedServer]: SpMino left the game
[06:04:50] [Server thread/INFO] [minecraft/MinecraftServer]: Saving worlds
[06:04:50] [Server thread/INFO] [minecraft/MinecraftServer]: Saving chunks for level 'world'/minecraft:overworld
[06:04:50] [Server thread/ERROR] [minecraft/MinecraftServer]: Exception stopping the server
java.util.concurrent.CompletionException: net.minecraft.crash.ReportedException: Exception generating new chunk
at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273) ~[?:1.8.0_252] {}
at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280) ~[?:1.8.0_252] {}
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:975) ~[?:1.8.0_252] {}
at java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:940) ~[?:1.8.0_252] {}
at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:456) ~[?:1.8.0_252] {}
at net.minecraft.world.chunk.ChunkTaskPriorityQueueSorter.func_219083_b(SourceFile:58) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.func_213148_e(SourceFile:83) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.func_213145_a(SourceFile:123) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.DelegatedTaskExecutor.run(SourceFile:91) ~[?:?] {re:classloading}
at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402) ~[?:1.8.0_252] {}
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289) ~[?:1.8.0_252] {}
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056) ~[?:1.8.0_252] {}
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692) ~[?:1.8.0_252] {}
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157) ~[?:1.8.0_252] {}
Caused by: net.minecraft.crash.ReportedException: Exception generating new chunk
at net.minecraft.world.server.ChunkManager.lambda$null$18(ChunkManager.java:529) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at com.mojang.datafixers.util.Either$Left.map(Either.java:38) ~[?:?] {re:classloading}
at net.minecraft.world.server.ChunkManager.lambda$func_223156_b$20(ChunkManager.java:516) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:966) ~[?:1.8.0_252] {}
... 11 more
Caused by: java.lang.NullPointerException
at net.minecraft.nbt.StringNBT.func_229705_a_(StringNBT.java:40) ~[?:?] {re:classloading}
at net.minecraft.nbt.CompoundNBT.func_74778_a(CompoundNBT.java:145) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:fml:randompatches:RandomPatches CompoundNBT Transformer,re:mixin,pl:accesstransformer:B}
at dev.itsmeow.betteranimalsplus.imdlib.entity.util.IVariantTypes.writeType(IVariantTypes.java:41) ~[?:9.0.1] {re:classloading}
at its_meow.betteranimalsplus.common.entity.util.abstracts.EntityAnimalWithTypes.func_184198_c(EntityAnimalWithTypes.java:30) ~[?:9.0.1] {re:classloading}
at net.minecraft.entity.Entity.func_70039_c(Entity.java:1309) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,xf:fml:quark:generic-update-hook,xf:fml:quark:override-collision,xf:fml:immersiveengineering:IE wire damage,xf:fml:randompatches:RandomPatches Entity Transformer,xf:fml:midnight:LadderNoises,pl:runtimedistcleaner:A}
at net.minecraft.world.chunk.ChunkPrimer.func_76612_a(ChunkPrimer.java:213) ~[?:?] {re:classloading}
at net.minecraft.world.gen.WorldGenRegion.func_217376_c(WorldGenRegion.java:250) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
at net.minecraft.world.spawner.WorldEntitySpawner.func_77191_a(WorldEntitySpawner.java:264) ~[?:?] {re:mixin,re:classloading}
at net.minecraft.world.gen.OverworldChunkGenerator.func_202093_c(SourceFile:56) ~[?:?] {re:classloading}
at net.minecraft.world.chunk.ChunkStatus.lambda$static$12(ChunkStatus.java:86) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.chunk.ChunkStatus$ISelectiveWorker.doWork(ChunkStatus.java:237) ~[?:?] {re:classloading}
at net.minecraft.world.chunk.ChunkStatus.func_223198_a(ChunkStatus.java:195) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.server.ChunkManager.lambda$null$18(ChunkManager.java:518) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at com.mojang.datafixers.util.Either$Left.map(Either.java:38) ~[?:?] {re:classloading}
at net.minecraft.world.server.ChunkManager.lambda$func_223156_b$20(ChunkManager.java:516) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:966) ~[?:1.8.0_252] {}

Appears to be a crash with Better Animals Plus.