I've had a bug occurring multiple times where after a player has picked up items dropped by a dead player they can no longer interact with anything and have to rejoin to fix it. I've seen reports of this happening in vanilla, although I do use mods and from what I've read the problem can either be from MoreCompany, Reserved Item Slots, or another mod interacting with those mods strangely.
If anyone has any insight on what causes this and how to possibly fix it I'd love to know, I've been wracking my brain testing different mod configs, uninstalling and reinstalling stuff, and more