Debug paste link:
https://pastebin.com/dy7U55mH

Description and relevant errors:

So occasionally when players are opening chests (crates in my server, plugin SpecializedCrates (don't know if its that crate plugin or ProtocolLib), they get kicked with an error:
https://pastebin.com/MBEBgcZ4

But as SpecializedCrates doesn't appear to be using ProtocolLib's features, can it even be the problem here?
Tested with one of the latest Paper builds and ProtocolLib's dev builds.

This is happening to me too when I sort chests with Inventory Profiles Next (only happens sometimes, not all the time).
It may also be happening to other players on my server that don't use that mod, but not confirmed.

Unless @KarlPro123 is using eco and/or EcoSkills then this is a ProtocolLib issue (if they are, then it may be an issue with one of those).

Yes I am using eco and EcoSkills, but don't know if this error is related to these plugins.
In my server it also doesn't happen all the time, but frequently enough to bother everyone.

Definitely not that crate plugin, as it happens randomly as well.

I get various versions of the same issue, one player was kicked while smelting, and several players get kicked when opening crates. I will say that I am also use Specialized Crates and eco as well.

You tried disabling it?

It wasn't kicking me earlier (no clue why) so I wasn't able to test it, I'll try it now.

I think this may have something to do with eco's rate limiter, though I'm not 100% sure.

# Window items packets have the option to be run asynchronously. This may cause
# some bugs and is considered experimental, however it has been tested without
# any apparent issues.
async-display:
  ratelimit:
    # If rate limit async display should be used.
    enabled: true
    # The amount of window items packets per timeframe needed to enable async display
    # for a specified player.
    cutoff: 4
    # The length of the timeframe in seconds.
    # Cutoff 5, Timeframe 1 means that if there are more than 5 window items packets
    # being sent per second for a player, then that player should have their packets
    # handled asynchronously.
    timeframe: 1

You tried disabling it?

You tried disabling it?

It wasn't kicking me earlier (no clue why) so I wasn't able to test it, I'll try it now.

Ok, tested it. Disabling didn't seem to change anything (it may have made it happen less but there is no accurate way to test that).

EDIT: I actually get a different error (extremely similar though) than the original: https://paste.srnyx.xyz/ejanemaloj.php