Please see link- shower drain pics, tile issues- I accidentally posted in plumbing...
Here is a link that might be useful: catastrophic bathroom
The hot mop was placed down before the preslope was done? What type of waterproofing was placed behind the walls?
It sounds as though there might be a lot more problems here than you think. I'm really thinking that the whole pan is going to have to be redone if what you wrote is actually correct. And maybe the walls, depending on the answer to my other question.
I'm sorry if I was unclear. The preslope was done, then it was hotmopped, then a mortar bed was laid above the tar. In other words, the floor tiles are not set directly on to the tar with thinset; there is a mortar base under them. The walls have wonderboard under the tile. I think there's green drywall behind that, or tar paper. Can't remember that far back.