Tried both the 3.8.0 quilt mod and the 3.8.1 fabric mod, when someone places an item inside the trinket hat slot while more than one player is within the rendered chunk, it causes the player equipping the hat to disconnect. For as long as there's another player inside that chunk, they cannot join back. If the other player leaves the server or leaves that chunk, it allows the trinket-wielder to dequip their hat and when the other player returns, it causes no issues as long as there is not a trinket equipped. This only happens specifically when there's other players within the surrounding chunk you're in.

This is the error it prints inside the game client:

This is the server log output when the user gets disconnected:

The client log outputs this when you get disconnected:
error.txt

The only mod I was using that interacts with Trinkets was Simple Hats, however I spoke with the dev fonnymunkey and they said it's most likely to do with trinkets and not their mod in particular, which I agree. Hope this is enough information to figure somethin out!!

Can you replicate this on fabric?