IMO the floor of the shower and the glass tile don’t work together and if the tile is cracking there was some issues with install ..If the waterproofing was done right this can’t be fixed by removing and replacing a few tiles that will affect the waterproofing envelope. What does the person who did the tiling think?

Thanks for your response Patricia. The installer has already replaced a few tiles. He said he doesn't think it will leak but it may crack more over time. To be fair, he advised against glass tile as he said this can happen, even with a proper install. Wish we had listened to him.

Not all glass tile is rated for wet areas. When it isn’t, the painted color coating on the back separates from the glass, and the glass becomes only lightly adhered in place, by the grout only. Plus, it‘s ugly. That appears to be what is happening with your installation .

Sometimes, buildings move with the seasons.

Wet season, ground absorbs moisture and swells, dry season, the ground drys and shrinks.

If you live in a building that moves with the seasons, your walls will move.

Big thanks to everyone for your comments - I really appreciate it. Here is the tile: https://www.tilebar.com/shop-by-colors-now/loft-super-white-frosted-4-x-12-glass-tiles.html. @User it says it's approved for shower wall use, but I agree with your take that the coating on the back seems to be separating from the glass. Any thoughts on why this might be happening? Maybe the wrong installation materials were used?