" The backer board is waterproof so it shouldn't be an issue." "

Famous last words. What is the backerboard?

GoBoard lightweight waterproof

Did you find a solution? I have same issues on a new construction. Tiles are absorbing water.

Photo of tiles absorbing water

ANSI TCNA call for 95% full contact mortar coverage w a wet area rated thinset. Cant tell in your photos if that was met. Id wager not.

Go board is waterproof as long as the seams are treated properly , theyve used a proper shower rated Thinset mortar (and not mastic) as well as a shower rated grout. You shouldnt have issues other than eyesores.

If you have big areas retaining water taking a longer time to dry out id want to rule out all these things as well as knowing 100% they didnt spot set these tiles which would be a tear out..

I use 511 Impregnator to seal my tile - not waterproof but resistant. Works well. Available at most home stores

https://www.amazon.com/Miracle-Sealants-Impregnator-Penetrating-Sealers/dp/B08L3P8PQL/

The tile installer came back to put 511 impregnator. Photo above is post sealer. Sealer helped but not 100 percent. Posting another photo before sealing . It was worse. I also tested sample of tile right photo. Dipped in water and you can see it’s dark gray. Installer assured me correct waterproofing was done. Now tile manufacturer has to come to inspect as tiles are defective and should not have labeled as appropriate for showers

@rah20, our installer came back and re-grouted the problem areas. You could visibly see the grout shrinking and cracking in most of the problem areas. So far it's holding up! 🤞🏻

So my bathrooms are getting demolished to replace the porous tiles on the wall 😞 nothing helped, 511 sealer did not work. So unfortunately it’s a complete demo. The question is the floor tiles ( these are fine they don’t absorb water) but should these be removed as well and replaced. I am concerned about if it’s not waterproofed properly around the floor? The drain is a “ channel” drain ( not in the middle). Contractor is telling me no need to remove floor tiles and he can install the wall tiles with no issues. Can you let me know your thoughts?

Wall waterproofing must tie in to the pan waterproofing, so yeah that floor comes out. I see nothing showing how they tied in together prior.

Yes you NEED it all removed.

I would also question the skill level, integrity and qualifications of anyone involved trying to tell you differently.

You also need a 48 hr. flood test BEFORE any tile goes in the shower. Be there when the plug gets pulled and the shower drains to make 100% sure there are no pools or birdbaths left in short order.