I noticed that my XP level dropped back from 26 to 23 this evening while I was AFK to watch a movie.
My purchased equipment is all intact so other than having a lesser number that doesn’t seem to have altered anything.
The level drop didn’t occur at the same time as my gems going into the negative, so it shouldn’t be related to whatever caused that either.
I would estimate that whatever event it was that culminated in the XP drop occurred in the last 3 hours. Sorry I can’t be more precise.
Anyway, not a game breaker. Just noting that it occurred for future reference and for people to watch out for, for reporting purposes.