It might also be worth trying to change the Local and RF protection states (not sure how to do that in smartthings though).
The symptoms you are seeing could happen if all the following conditions are met:
- Local control is set to No Operation Possible
- RF Control is set to No Operation Possible
- Relay is disabled
- Dimmer is set to turn back on after power is restored
Of course, it wouldnt explain HOW all those settings got changed, but its worth a try. As long as both Local and RF control is set to No Operation Possible, the dimmer will not respond to any commands. Factory reset will probably fix it too, but you would end up having to re-include.