Where a grout-only shower goes wrong
Tile and grout shed water, but they do not stop it. A shower set straight onto drywall or cement board looks exactly the same on the day it is finished as one built properly, and the difference only shows up later.
Water gets through a hairline in the grout and into the wall, and nobody sees it. By the time a tile loosens, a corner stains or the floor outside the shower feels soft, the damage is already behind the wall.
That is why a shower that was tiled over the wrong layers is rarely a tile problem. It is a wall problem, and the fix starts with opening the wall.
