Hello
@RBQ, after ONE UI5.1, I reset my Sleep Mode by cancelling the current setup and starting afresh. Working one day at a time I set Bed Time and Wake Time for Monday and made sure Wake Alarm was Off. Then did the rest of the week day by day. It seems to be working so far, but it before 5.1 it would work for a couple of days and then reactivate again. So I'm not convinced I have a resolution yet.
I'm using to run a Routine to shut everything down to save battery overnight. It's just an instant shock when it suddenly kicks in unexpectedly.