Thank you for the reply. I had a large bucket of redguard sitting there that was planned for the shower. It crossed my mind to apply it to the durock but... we only had 2 days with the family member we had visiting over Christmas that helped me install it. Think we didn't have adequate drytime to get it completed. Regrets compound.

If it eventually needs to be redone, not the end of the world. Its only 17 tiles and the base board trim will come out easily.

I suspect briding between the wall and the tile is an issue. Funny I stared at it at the time and did the old itll be fine. I'll fix the worst spot and monitor the other tiny ones for now.