Improper substrate preparation. I'd wait another year and have all the cracked ones replaced simultaneously. Maybe it'll self-destruct by then.

Any photos during construction? Any ideas what is behind the tile?

I have a few photos.

With your initials and the photos now I think this may be a joke post. The prep can't actually be that bad. If this is in fact a real post with that prep it is 100% a complete tear out, and do it now before your house gets further damaged.

Not a joke post. Can you tell me what you mean by that?

I took the pictures because I thought it looked odd, but I’m not trained.

You have no waterproofing and the shower is structurally unsound. The only solution is to gut and rebuild with a different contractor.

Not our only option since it’s still under warranty.

"Not our only option since it’s still under warranty."

Actually it really is the only option as what is there cannot be fixed.

You're going to have water penetration through those unsealed joints under the tile that will rot the framing (no grout is waterproof). I was also going to say that you can't simply replace individual tiles without compromising the integrity of the waterproofing, but it appears from your photos that the waterproofing was incompetently done, so that probably can't get any worse. Sorry to be negative, but that's a disaster and needs to be completely re-done.

Thanks for your input. We’re going to have to fight to have it torn out.

No, we’re not. We’re just going to have to fight to have them pay for it. It’s a giant mess and now that I know more about it, I’m shocked that a company would even do this. It was an expensive renovation and we trusted them. It’s sad.