Happened three times to me today. I'm unaware what's the exact cause/trigger, but as mentioned in the title, in each case it happened, it was when a predator run up to me in the salt mines.
Two of those times I was wearing the lobby's leader crown. Not exactly fun to lose it due to a game-crushing bug for sure - but while I can't be certain, I think it happened without the crown in the third case, possible excluding that being related to the reason behind it.
(hopefully I'm not reposting a known bug - didn't get any results when searching for "runtime error" on the forums)