There was a thread on this a few weeks (months?) ago. Several people, at least, reported that expert mode was getting unchecked for some unknown reason. I was one of them, and I was surprised to find it unchecked (and relieved that it was a simple fix). Like the OP, it wasn't my doing.

(Mind you, the OP's problem appears to go beyond this, since the OP rechecked the Expert setting.)