Server Crash (Exception ticking world: ConcurrentModificationException)

Description: Exception while ticking

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
	at java.util.HashMap$KeyIterator.next(HashMap.java:1453)
	at yw.a(SourceFile:983)
	at bpa.a(SourceFile:281)
	at bpa.a(SourceFile:351)
	at bwr.d(SourceFile:105)
	at bxe.a(SourceFile:49)
	at cei$a.a(SourceFile:856)
	at yw.b(SourceFile:609)
	at yw$$Lambda$3827/659711812.accept(Unknown Source)
	at bpn.b(SourceFile:84)
	at yw.a(SourceFile:351)
	at net.minecraft.server.MinecraftServer.b(SourceFile:893)
	at net.minecraft.server.MinecraftServer.a(SourceFile:832)
	at enr.a(SourceFile:89)
	at net.minecraft.server.MinecraftServer.run(SourceFile:691)
	at java.lang.Thread.run(Thread.java:745)