The wall surface could have been irregular with humps and dips in it.
Tiles bulging off wall.
The wall isn t hot to touch difficult one to answer as obviously the shower is running at the time but the problem does occur on the side of the hot water upright feed each time.
B replace the removed tiles with a large mirror c force the wall back in with some type of ugly metal alloy strip screwed in over the top of the tiles and into the stud.
If no adhesive is applied then the tiles will fall off.
The chalk dust will stop the tiles from adhering to the wall.
The adhesive is called supergrip ceramic tile premix adhesive as recommended by the tile shop and the grout is wateproof grout used for swimming pools again as recommended by the tile shop where the tiles were bought from the ceramic tile centre in portsmouth.
Tiles need to adhere to a smooth undamaged surface.
Damage to a subfloor is one of the most common reasons for a tile to bulge or lift from the subfloor according to the american society of home inspectors.
Make sure that the tile adhesive that you use is water resistant.
I feel this in conjunction with skinned over adhesive is the root cause of your tile failure.
A pull down that section of wall and re tile with new blue board etc although the current old tiles cannot again be sourced to match the exisiting.
The adhesive needs to be applied evenly and on every tile.
As ceramic tile get larger the wall or floor surface must be flatter and flatter.
The subfloor must be clean even and dry before tile installation.
Adhesive has not been applied properly.
Grouting has been done too early.