Since the tile is flat and in the same plane the wall surface must also be a perfect match.
Tiles bulging off wall.
As ceramic tile get larger the wall or floor surface must be flatter and flatter.
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.
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.
Any low spots on the subfloor can cause a tile to bulge.
Grouting has been done too early.
Adhesive has not been applied properly.
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.
The wall surface could have been irregular with humps and dips in it.
I feel this in conjunction with skinned over adhesive is the root cause of your tile failure.
Make sure that the tile adhesive that you use is water resistant.
If no adhesive is applied then the tiles will fall off.
The chalk dust will stop the tiles from adhering to the wall.
Tiles need to adhere to a smooth undamaged surface.
The adhesive needs to be applied evenly and on every tile.
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.