Put river rock on shower foor now grout is cracking and hair line cracks all through it is there a certain type of grout that should have been used for river rock

Where did you get the river rock? River rock is a natural substance and if you got it from natural sources it would not have been sterilized to use in that application, nor 'roughed up' a bit to accept the grout.

River rock needs a sealer first, with a 24 hour wait at least. Then it needs urethane grout, and you have to apply it with skill, troweling it on and using a float at first, then smoothing it by hand, and yet not making it too thick in depth. Curing time after grouting should be at least 2 days for a shower base.
Depending on what's under the rock, I might rip it all out.

I set rock in my shower floor. The contractor built the new shower pan for me however he had left gaps; the end of the walls did not meet the top of the pan. I added a layer of Thinset over the cement to build up the pan and cover up all the gaps, and to add a better angle for drainage. I let this dry for like two weeks; it seemed to take forever to set. Before the Thinset was completely dry I added the sheets of rocks and added individual rocks to fill in. After all was dry I grouted the shower and the floor, let that dry for a few days and had to regrout because the first grouting was not thick enough and flowed out of some of the seams. I let this dry for 2-3 days, then sealed the entire shower. I let that dry for another 2 days. Everything seemed fine. I've been using the shower for about 2 weeks. Yesterday I noticed a loose rock... then another... then began peeling rocks/grout up until I'd pulled up a huge hole. The glue that was used to adhere the rocks to the webbed-sheets is really gummy. The Thinset under the webbing sheet is rubbery on top and feels a little 'squishy' underneath, but not a lot. I did a rock floor in my other shower but didn't have any problem like this, but then I didn't have to add a thick layer of Thinset to the top of the cement. I'm assuming I'll need to tear up all the rocks and grout. Then what? Should I seal the Thinset before I put rocks down again? Then seal the rocks? Then grout and seal again? And what kind of sealer? I used sanded grout, premixed. Thank you in advance for your help. It looked really nice... for 2 weeks!