Waiting to see if I get a better response from MS than "Backup and reinstall"
I doubt that you will, and I have to say, that in really strange, idiosyncratic instances were inexplicable behavior that no one can reliably replicate occur, "nuke and pave then restore user data from backup," is the best and most appropriate response.
Anyone who has owned their own automobile has experienced at least one of the following things:
1. Some misbehavior that keeps recurring, until we take it to the mechanic, at which point it stops, and it won't recur for the mechanic. The best that can be done is a cursory evaluation for "something obvious," but if that's not found, there's nothing that can be done at that time.
2. The response, "They'll do that," in one form or another, usually followed by a simple fix that we want to slap ourselves for not thinking of, or a statement that, "You could fix it, but that would cost {insert insane figure here}, and leaving it that way will cause no damage."
3. The thing happening stops and no one knows what it actually was, why it occurred, or why it stopped.
Stuff like "automatic reversion to S Mode" is, to my way of thinking, almost certain to be a "Category 3" occurrence. Some confluence of events that might never recur again on that machine, and that required some insanely long series of events to trigger in the first place, making backward tracing utterly impractical, is at play. Nuke and pave is the appropriate way to solve these, as the cost in time, money, sweat, tears, cursing, lost availability, and the list goes on is far higher were one to try to diagnose a root cause, which likely wouldn't help in any practical way, anyway. This business is about getting the best possible (note, possible) solution in the best possible amount of time. That means you don't try to figure out every failure. It's not cost effective for any party involved.
