Not exactly crazy but just mysterious…this was at a software company I worked at many years ago. It was one of the developers in the team adjacent to ours who I worked with occasionally - nice enough person, really friendly and helpful, everyone seemed to get on with them really well and generally seemed like a pretty competent developer. Nothing to suggest any kind of gross misconduct was happening.

Anyway, we all went off to get lunch one day and came back to an email that this person no longer worked at the company, effective immediately. Never saw them again.

No idea what went down - but the culture at that place actually became pretty toxic after a while, which led to a few people (including me) quitting - so maybe they dodged a bullet.