i've been trying to post a pic!

I have no idea, but I am interested to read what others think!

Is the worst of it along that one row, or is there a bigger area than this?

that's the worst of it, but there are other patches along that wall. It's so ugly!!

Did they install the tile using a wire mesh lath? My only guess would be that it is rusting (although it shouldn't be, especially being so new), or maybe some nails behind it are rusting, and then bleeding through the cracks.

Either way, you have water behind there

@Mark... oh no!!!!!!! Do you have any theories on what it could be? I am sitting down.

and @CLC... I have no idea, since we bought it after it was redone.

Leaking supply pipes? Leaking drain pipes? Leaking roof? Leaking air conditioner condensation line misconnect? Animal Octoberfest? . . . . .

The builder would probably be the first person that would be able to tell the cause of your concern. Because of the time that passed, you will most likely bear the burden of the expense. People here can only guess, someone there can give you answers.

Clean it after the builder has a chance to inspect it, you may be washing away vital clues.

Mastic reemulsifying. Plus the mold that is growing on the organic mastic that should not have been used. I have an idea that the contractor never heard of a rain screen either.