How was he able to change the five rows without compromising the waterproofing behind the tile? Did he even waterproof behind the tile since tile and grout are NOT waterproof?

And just as important, why did the tiles crack?

Thank you for the response @cpartist! He said he redid all the backing behind it and put in extra measure to prevent cracking. We used the Schluter system for the walls and pan. He doesn't really know why the tile cracked in the first place. He said it was probably due to "crazing" - a defect in the tile during production. The shower has not been used since the initial tile install, so there can't be any water damage going on back there yet (I don't think). And the tile batches from the original install and the redo were the same.

Tiles can have different dye lots. Since they were installed at different times, I assume they were purchased separately. I doubt they will ever change color to match the existing tiles. Sometimes stone or glass tiles will differ in color if the mortar is gray vs. white, but I’ve never heard of it happening with porcelain or ceramic tile. Sounds like a load of BS to me.

Thank you for the response, Susie! The tile batches from the original install and the redo are the same, but they were in different boxes. I don't know if that makes a difference or not. :(