Mine started doing thattoo not long ago but I also noticed that it appeared when I was having trouble with the left bag not opening. Have you had that issue? It has been common and you can search the forum for related issues and fixes. My sensor problem went away when I did a little bending of the latch opener mechanism.
Have a peek in just as the lid is almost closed to see if the latch is entering the lock dead centre. The latch tends to bend very easily, especially when the pannier is loaded fully and the latch can actually miss the lock. You end up with a closed pannier held by one lock whilst the other is not in the lock at all. I have had to adjust mine a few times by bending it slightly. I bent the rear box one so many times that it eventually snapped in two, so I carry a spare set of latches in the pillion pocket just in case. It has to enter the lock in the centre to operate as it should.