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Internal Exception: java.util.ConcurrentModificationException

java.lang.ClassCastException: class net.minecraft.server.network.ServerGamePacketListenerImpl cannot be cast to class net.minecraft.network.protocol.game.ClientGamePacketListener (net.minecraft.server ...
GitHub

Internal Exception: java.lang.IllegalArgumentException: Registry ResourceKey[minecraft:root / apoli:configured_entity_condition] was missing

I'm unable to replicate this with purely the base Origins, but I'm going to try downloading a larger Origins pack (Origins++, ik you're the maintainer of it, and you're probably reporting this based ...
The Droid Guy

How To Fix Minecraft Internal Exception Java.IO.IOException Error

Are you getting the frustrating “Internal Exception Java.IO.IOException” error when playing Minecraft? This problem affects a lot of players because it can be ...