The following things happened:
- A few months ago I posted an answer on Skeptics (10 k only).
- That answer received thirtysomething upvotes (and got me this badge.
- A few days later that answer was deleted and all the reputation I gained from it was voided.
- Since I had no other answers or comments, my reputation went back to 101 (here is my reputation-, question- and answerless account).
- Yesterday, I received a top-bar reputation notification for −10 with reason “User was removed” on Skeptics. My reputation stayed at 101, however. Since I did not actually lose any reputation, I consider that reputation notification a bug.
I can only guess that the last event was caused by the removal of some user who had voted on my deleted answer.