Just for me, I never had that happen. I did have one quit working completely and had to be replaced, but never had it move. I believe mine was attached somehow to my chest muscle, but not for sure how that was done. We did have one lady on the site that had her's move, it slipped down somehow.
It should be a fairly easy fix, even if they have to do a small incision to fix it.
Hope you get it fixed, I know they are great to have.