An error seems to occur when generating/loading chunks,, my guess is that manipulation of an Immutable collection is happening - As the stacktrace seems to suggest.
Stacktrace:
[23:35:34] [Worker-Main-10/FATAL]: Failed to schedule load callback for chunk [-233, -362]
java.util.concurrent.CompletionException: net.minecraft.server.v1_16_R1.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.server.v1_16_R1.ChunkTaskQueueSorter.b(SourceFile:58) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.ThreadedMailbox.e(SourceFile:94) [spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.ThreadedMailbox.a(SourceFile:137) [spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.ThreadedMailbox.run(SourceFile:105) [spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
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.server.v1_16_R1.ReportedException: Exception generating new chunk
at net.minecraft.server.v1_16_R1.PlayerChunkMap.lambda$26(PlayerChunkMap.java:551) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at com.mojang.datafixers.util.Either$Left.map(Either.java:38) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.PlayerChunkMap.lambda$24(PlayerChunkMap.java:536) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:966) ~[?:1.8.0_252]
... 11 more
Caused by: java.lang.UnsupportedOperationException
at com.google.common.collect.ImmutableMap.clear(ImmutableMap.java:620) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.ChunkGenerator.updateStructureSettings(ChunkGenerator.java:309) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.ChunkGenerator.a(ChunkGenerator.java:233) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.ChunkGenerator.createStructures(ChunkGenerator.java:212) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.ChunkStatus.d(SourceFile:51) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.ChunkStatus.a(SourceFile:219) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.PlayerChunkMap.lambda$26(PlayerChunkMap.java:538) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at com.mojang.datafixers.util.Either$Left.map(Either.java:38) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at net.minecraft.server.v1_16_R1.PlayerChunkMap.lambda$24(PlayerChunkMap.java:536) ~[spigot_1.16.1.jar:git-Spigot-758abbe-2b00831]
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:966) ~[?:1.8.0_252]
... 11 more
Thank you for your report!
However, this issue is Invalid.
Your game, launcher and/or server is modified.
If you can reproduce the issue in a vanilla environment, please create a new ticket.
Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang Studios or the Bugtracker.
Any plugin or resource pack issues need to be addressed to the creator of the plugin or resource pack.
If you have problems on large servers, such as The Hive and Hypixel, please contact them first as they run extensively modified server software.
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