It was Skype. Skype changes Windows defaults!?!? Apps should never do this. At least ask first; give some kind of warning. I've wasted a whole day tracking this down. The solution: uninstall Skype. And that's my final answer. It stays off. Good riddance.
Message to Skype: "This is my computer. It's my OS. I configure it."
After restart my settings remain, because that's what setting do, they get set and bloody stay set. And yes I tried everything to get Skype to play nice. Only uninstalling made a difference. Yes I already tried "that" (whatever you are about suggest), remember all day, 12 hours of my life sucked away. But now all my other audio apps work fine. They get along. They don't break each other. They access various audio devices without changing OS defaults. What a concept.