Newbie - old concrete pool problem

New to the forum and after reading my initial post I felt it wasn't very clear - Sorry! Let me try again - I restored this concrete pool two years ago and upon opening this year I found that many of the top most tiles popped off. I found that there is a pretty distinct horizontal crack below the coping (between the coping and the beam). The last time I restored this I simply tiled over the crack. I didn't fill the crack either. To prevent this from happening again I was hoping for some guidance on a few ideas. 1) should I fill the crack and if so with what material - silicone? other? 2) To fix the tile being attached to two separate surfaces (above and below the crack) could I simply use epoxy on the tile and wall below the crack and either not use any adhesive at all above the crack or maybe silicone so that if there is shifting it would be flexible and potentially not pop off? As some additional information I did replace the material in the expansion joint between the deck and coping in case this was allowing water under the coping.

I'm no expert on concrete installations but it sounds like you either have had some ground movement or you are having some other instability. Your early repairs may have failed due to that or to adhesion problems. Was the surface properly prepared before the tiles were installed?

Maybe one of our pool installer experts can help you.