See:
In short you need to unplug ST hub and if you have V2 remove batteries for at Least 15 min then plug back in. It will take up to a day to rebuild the mesh.
Your issue with the outlet / motion is likely that the outlet was the only repeater that the motions sensor was on. So when the outlet came back up it was found again. You could reduce the odds of this happening again by using multiple repeaters at the same distance and rebuilding the mesh.