How old are the tiles and the grout? How long ago did they become stained?

I’m not sure I’ve been in this house for 6 years. I think the old owners updated it before selling it. About 9 months ago it stained

What have you tried to remove the stains?

Because of the similarity in color. It just suddenly appeared and it seemed like the color was leaking from the grout. We tried bleach and some other commercial cleaners

Again, Is that a missing tile in the very corner?

No I rechecked there is no missing tile. But I just found out that the brown color grout from the wall tile mixed with some white chalky caulking along the edge of the wall of the floor which we put to seal a leak on the floor. And the brown stain appeared a few days after that. Seems like some chemical reaction happened

Is this inside a shower?

No idea, but why does the grout on the red tile appear to be different colors, some black and areas more gray. That red tile is very cool!

Yes inside a shower

I’m not sure about grout colors being black and gray. We purchased the house this is how it was

"seal a leak on the floor."

That may be the stain, rust from the fasteners behind the tile. You are looking at the very least selective demo but probably a gut job if that is the case.

Thank you

They bandaided a leak. Which you cannot do. Very shady behavior. A leaking shower is a failed shower, that needs replacement.

From your post, it appears that you sealed a leak after moving in?

What kind of leak was it. My non-pro understanding of shower waterproofing is that the waterproofing isn't seen as it is below the tiles. Neither tile nor grout are waterproof. I think caulk has a bit of a waterproofing effect but that would depend on where it is used.

Where was the leak?

If you have a leak below the tile and put some kind of sealer on top of the tile, that very well could be rust and mold seeping up from underneath trying to find a way out and being stopped by the sealer. If you sealed over that tile, then the discoloration would appear to be below the sealant, so no wonder nothing will remove it. Can't get to it through the sealer.
It would seem you have a bigger problem than discoloration in that shower.

Thank you we are hitting it out

Sorry meaning gutting it out