The bug
Today I was generating and testing worlds on 21w07a and then I loaded some chunks. But then my game went unresponsive and crashed. This was also happening on a server today too with the worker threads dying.
Stack trace
21w19a\: [^crash-2021-05-18_18.42.52-server.txt]
Description: Accessing PalettedContainer from multiple threads
java.lang.IllegalStateException
at ahc.a(SourceFile:27)
at ahc.a(SourceFile:19)
at cml.a(SourceFile:50)
at cml.a(SourceFile:109)
at cmf.a(SourceFile:66)
at cmf.a(SourceFile:60)
at cmm.a(SourceFile:179)
at abr.a(SourceFile:229)
at bwg.a(SourceFile:15)
at ctn.c(SourceFile:141)
at cya.a(SourceFile:75)
at cxv.a(SourceFile:120)
at cxv.a(SourceFile:165)
at cxv.a(SourceFile:92)
at ctn.a(SourceFile:98)
at ctn.a(SourceFile:152)
at cqv.a(SourceFile:55)
at crb.a(SourceFile:29)
at java.base/java.util.stream.Streams$StreamBuilderImpl.forEachRemaining(Streams.java:411)
at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762)
at crb.a(SourceFile:28)
at cqv.a(SourceFile:55)
at crb.a(SourceFile:29)
at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625)
at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762)
at crb.a(SourceFile:28)
at cqv.a(SourceFile:55)
at crb.a(SourceFile:29)
at java.base/java.util.stream.Streams$StreamBuilderImpl.forEachRemaining(Streams.java:411)
at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762)
at crb.a(SourceFile:28)
at cqv.a(SourceFile:55)
at bwx.a(SourceFile:382)
at clv.a(SourceFile:245)
at clx.c(SourceFile:100)
at clx.a(SourceFile:231)
at aay.a(SourceFile:563)
at com.mojang.datafixers.util.Either$Left.map(Either.java:38)
at aay.a(SourceFile:557)
at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1146)
at java.base/java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:478)
at aba.b(SourceFile:58)
at aqh.f(SourceFile:92)
at aqh.a(SourceFile:132)
at aqh.run(SourceFile:100)
at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1434)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:295)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1016)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1665)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1598)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)
Linked issues
is duplicated by
relates to
Attachments
Comments

Can confirm
Does this bug still happen as the Height limits have been reverted?

Just got hit with this in 21w17a, can confirm.

This bug still affects 21w18a. Please reopen.
In that case, please file a new bug report and attach an up-to-date crash report.

Please attach a new crash report if this is still an issue.
They gave one the day after this bug was fixed, it's locatable in the history tab in activity on the Thursday, may 6th, 1 day after this bug was supposedly fixed.

21w20a crash report attached
Hi! Could you please attach the full server log with the crash on the latest snapshot? It should contain more debugging information that should help us track down this issue
Second time this has been fixed
encountered this in 1.17.1. this was not vanilla, 17 mods plus fabric, and 1 datapack. I don't read code so, I just don't know if it's one of them. Attached crash report

The bug tracker does not accept issues experienced using a non-vanilla client, so unfortunately we cannot help you.
The same stack trace can be seen here MC-216214. Marking as relates for now.