The subfloor must be clean even and dry before tile installation.
Tiles bulging off wall.
The adhesive needs to be applied evenly and on every tile.
Any low spots on the subfloor can cause a tile to bulge.
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.
Grouting has been done too early.
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.
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 chalk dust will stop the tiles from adhering to the wall.
A buckling or partly raised tile on your shower wall usually means water has gotten behind the tile often through cracks in the grout and caused the wall material to expand pushing the tile outward.
Since the tile is flat and in the same plane the wall surface must also be a perfect match.
Adhesive has not been applied properly.
As ceramic tile get larger the wall or floor surface must be flatter and flatter.
Make sure that the tile adhesive that you use is water resistant.
If no adhesive is applied then the tiles will fall off.
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.