When I setup MN, it was showing "watchdog expired" status initially. sentinel was working fine (no error). I just restarted the controller wallet and left it like that thinking that I will check it later. Noticed that after few hours, status automatically changed to "Enabled" (after 8 hrs I think).  No idea how it worked, but its my experience. setup is 2+ days old and  I received 3 rewards so far