ConcurrentModificationException during worldgen

What I did, in order of execution:
1. Created new world
2. Disabled VSync
3. Changed brightness to maximum
4. Disabled FPS limit
5. Ran a little

java.util.ConcurrentModificationException
	at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1225)
	at dam.b(SourceFile:63)
	at dam.a(SourceFile:53)
	at com.mojang.datafixers.util.Either$Left.map(Either.java:38)
	at cvy.a(SourceFile:84)
	at cvy.a(SourceFile:109)
	at cvv$c.a(SourceFile:141)
	at cvv$c.a(SourceFile:54)
	at cvv.a(SourceFile:305)
	at cqv$a.a(SourceFile:49)
	at cqv$a.a(SourceFile:35)
	at csb.a(SourceFile:277)
	at cpn.a(SourceFile:36)
	at cku.a(SourceFile:296)
	at cku.a(SourceFile:279)
	at ckw.e(SourceFile:53)
	at ckw.a(SourceFile:231)
	at aas.a(SourceFile:563)
	at com.mojang.datafixers.util.Either$Left.map(Either.java:38)
	at aas.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 aau.b(SourceFile:58)
	at aqc.f(SourceFile:92)
	at aqc.a(SourceFile:132)
	at aqc.run(SourceFile:100)
	at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1429)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
	at java.base/java.util.concurrent.ForkJoinPool$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)