As i said before, to look at those pictures I myself would think dodgy subfloor and prep, the only movement affecting the tiles is the natural expansion and contraction of the floorboards.
I almost think not gluing the hardiebacker down as I always do would have prevented this?
But tiles are not best but .they not in my mind suitable for a floor as with most ceramic tiles they are glazed.a thin miniscule cost cutting amount of it in most bct tiles .you get the ceramic that might be able to withstand the .flexibility issues .then a half mm glaze of colour etc that is fired separately onto the ceramic tile .I don't tile most ceramics on floors as your asking for trouble .
I saw a 12 year old bathroom with polished porcelain dot and dabbed straight onto floorboards riddled with woodworm, not a crack in sight apart from one tile put that was sinking into the void as the floorboard was dust.
That picture looks like it was done on ply .the ply has shrunk in size .the glue is good so the weak point is the tile and it cracks in a straight line .so close to edges of tile .it's definitely weak tiles and no decoupling membrane