David Ray

This seems to be working now in the latest version 1.16.4

This is happening with 1.14 as well.  Vanilla 
has made the advancement [Fishy Business]

[20:25:05] [Server thread/WARN]: Failed to handle packet for /IP:PORT
m: Ticking player
at vh.i(SourceFile:450) ~[vanilla-1.14.jar:?]
at vy.b(SourceFile:194) ~[vanilla-1.14.jar:?]
at ja.a(SourceFile:243) ~[vanilla-1.14.jar:?]
at vx.c(SourceFile:171) [vanilla-1.14.jar:?]
at net.minecraft.server.MinecraftServer.b(SourceFile:842) [vanilla-1.14.jar:?]
at ug.b(SourceFile:343) [vanilla-1.14.jar:?]
at net.minecraft.server.MinecraftServer.a(SourceFile:764) [vanilla-1.14.jar:?]
at net.minecraft.server.MinecraftServer.run(SourceFile:632) [vanilla-1.14.jar:?]
at java.lang.Thread.run(Thread.java:813) [?:1.8.0_192]
Caused by: java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1445) ~[?:1.8.0_192]
at java.util.HashMap$KeyIterator.next(HashMap.java:1469) ~[?:1.8.0_192]
at java.util.AbstractCollection.addAll(AbstractCollection.java:343) ~[?:1.8.0_192]
at java.util.HashSet.(HashSet.java:120) ~[?:1.8.0_192]
at com.google.common.collect.Sets.newHashSet(Sets.java:273) ~[vanilla-1.14.jar:?]
at ajj.b(SourceFile:198) ~[vanilla-1.14.jar:?]
at ajj.g(SourceFile:180) ~[vanilla-1.14.jar:?]
at ajj.e(SourceFile:170) ~[vanilla-1.14.jar:?]
at aio.cI(SourceFile:1321) ~[vanilla-1.14.jar:?]
at vh.i(SourceFile:421) ~[vanilla-1.14.jar:?]
... 8 more