You have a bigger problem than you think. Tiles don't just start peeling apart without something else being wrong. See how the tile ends just short of covering the wall it is sitting on? That is terrible workmanship and it may have ruined your wall. Walls such as this in a wet area are supposed to be covered with a solid piece of material with no grout lines. Grout is not waterproof. The solid surface is supposed to overhang the wall so that water can flow down to the bottom edge of it and drip off, without flowing back to the wall. Water can have wept into your wall through the grout and the seam where the tile ends. My guess is that your tiles that are peeling are sitting on a sopping wet wall.

I have the same problem with newly installed tile but a different brand. The bullnose was treated with some type of epoxy which is peeling. What was the outcome of your problem?