Funny how we always have the same problems...
This happened to me a couple of years ago except my tiles were migrating
under the cabinet and shower stall. This left a very noticeable gap with the next tile.
I ordered 6 new tiles from our friends at Lichtsinn, thinking it would be happening to more tiles. I just carefully cut away the moving tile at the edge of the cabinet & shower, then trimmed a new one to fit. Frankly, I thought the movement might continue and the problem would reoccur. That was at least 2 years ago and so far so good - no more movement on the ones I replaced and no new areas of movement. I'd like to blame it on bad adhesive or bad installation of the originals, but why would we have the failure in the same place?
As the DW and I always say, "It's all part of the adventure!"
Sometimes I could use a bit less adventure...