Curb movement like that is typically from a wood-built curb (stacked 2-by lumber, for example) that is absorbing moisture and expanding/swelling. How is moisture getting to the curb? Could be one of several things. Not sure how conscientious the installer was in terms of making sure the shower pan membrane is sloped (versus laying the membrane flat on a flat subfloor), or how he detailed the membrane over the curb. It's possible there are nails through the top or inside faces of the curb (and thus through the membrane) and moisture is getting through the nail holes. It's possible that he built you a perfect curb but used wet pressure-treated wood and the PT wood is warping as it dries. Or your house is on a slab, and he put the wood right on the slab. Moisture through the slab is causing the wood curb to expand. So it could be one of several things. It should be fairly easy to diagnose though, as the tiles are popping off on the outside face of the curb. They'll have to be removed eventually to diagnose and repair. When they are removed, take a look to see what's in there. Post photos if you can. To give you a bit of an education as to how a typical CPE-membraned shower with a wood curb is built, check out Harry's pictorial. Note that Harry's membrane is "draped" over the wood curb. That there are no nails/screws on the top or inside face of the curb. That the lathe (wire mesh) is bent in a "U" shape and it's simply the inverted "U" bends that hold it over the curb. Again, there are no fasteners through the lathe and into the top or inside face of the curb. I have seen instances where the membrane gets draped over the wood curb, then the installer nails cement board on the three faces of the curb and tiles on the cement board. Not good. Again, nails through the membrane on the top and inside face are a no-no. I don't see screws through the bottom track of your door frame that go into the curb. That's good. Best, Mongo

if the installer looselayed and nailed the cement board without a thinset base under it, your entire tile installation is incorrect and compromised because he did not give the backerboard a solid base to begin with by electing to looselay it, which is the incorrect method of installing cement backer board. the correct method(s) of installing cement backer board is in a minimum troweled 1/4" bed of thinset mortar UNDER THE BOARDS and nailed or screwed every 6"-8" and within 1-1/2" from all seams, and some manufacturers allow a bed of high strength construction adhesive UNDER THE BOARDS with the same anchors and naiing pattern, so check with the manufactrer for specifics). This gives the tile system a solid foundation to prevent movement and to flatten or level any minor subfloor inconsistencies that may cause movement in the system that can crack or debond tile and/or grout joints. Loose laying and screwing is insufficient and does not provide that solid foundation so it would be prone to movement that can cause cracks, tile pops, debonding, and/or cracking grout joints. The tiles and cement board needs to be gutted down to the bare subfloor, and the cement board anchored properly, or you may have more problems even worse than what you have now. Basically everything needs to be gutted and reinstalled properly or new product purchased and installed properly if they can not be gutted intact and usable. If that isnt feasible for you or your workers, then any repairs may be a waste of time, quite temporary, and plan on revisiting this issue time and time again over the years. Here is some information on CORRECT installation of cement backerboard systems: How to install Cement Backer Board In my opinion, your should demand the contractor with 30+ years experience gut all his tile and backerbaord work, install new the backerboard properly, then the rest of the tile work, PLUS foot the bill for anything that is damaged or uninstallable because of damage during the removal process ... because he did a crappy job and must guarantee his shoddy workmanship. If he refuses, you may have civil recourse becasue his work is improper. as to removing everything unhamed ... good luck ... i dont think its possible because everything is attached and locked in with thinset. If you must try delicate intact removale, jsutt go slow and pry lightly with just enough force to bring it up, but again, its improbable becasue you are talking cured thinset, so i doubt the matting will survive.

I kinda figured out what's happening actually. the cracks in the grout were only the beginning. the top row of large format tiles which were vertically oriented actually are buckled. this is at the seam between the old house and the new house. is not obviously structurally unsound but must have settled... either that or the Hardie board was installed crooked causing strain... i should have put smaller tiles or placed the tiles horizontally. probably high enough not to be a major leak concern. I'll observe this for a few months. the grout cracking actually looks more like shrinkage to me but they should have used caulk. people are just telling me to caulk over it rather than chiseling out the grout. all the floor leveling issues were caused by trying to make new sister joists across the floors, but not being able to change out the old joists which are embedded under the walls. the old and new joists were milled at different sizes (cannot get match) so it caused some discrepancy. again not structurally dangerous but annoying. not sure if it's worth fixing but I'll get a different structural engineer and a leveling company to look at it. so same underlying cause, different symptoms. in another post I noted the stairs cracking. this was just general crappy cosmetic workmanship and not structural. what a pain in the @$$

From here it looks like the shower was not properly waterproofed and the pony wall is swelling due to the wood getting wet. Testing for moisture levels outside the shower may help, right before you remove the drywall from the outside of the pony wall to check for waterproofing (if any) and leaking.