Jump forces the cursor mode, so that makes me wonder if it’s an issue with freezing while doing something that requires the cursor, which might explain why we’ve been have this issue so much. So maybe today we’ll try to never switch characters or anything to freeze the game while the other is jumping, targeting enemies with the cursor, finding a location to summon or throw, etc.
I’ll add that I think the bug occurs most often when both players are simultaneously taking their turns in combat. Then:
Player A is not currently in control of their character due to being mid jump, character swap, or desummoning a mage hand/minion.
Player B triggers an action that causes a freeze - switching their character, summoning something, etc.
Player A’s character then loses the ability to target things other than with the left/right pad. I don’t think they can move either.