Make sure you're doing the following

• You're using the latest build for your server version
• This isn't an issue caused by another plugin
• You've checked for duplicate issues
• You didn't use /reload

Describe the question
whenever player claims any rewards from mobs killing or battlepass etc or mythic mobs... they get kicked with set container error from protocol lib
https://mclo.gs/Il5b8ZE

API method(s) used
List what API method(s) you're using

Expected behavior
Shouldn't be kicked

Code
If applicable, add relevant code from your project

Additional context
Add any other context about the problem here.

Some plugin (not ProtocolLib) is sending an ItemStack/Inventory and while doing so modifying a list which in turn triggers a ConcurrentModificationException. Only thing you can to is try to remove plugins one by one until the error no longer occurs.