How to fix soggy shower wall?

You should remove the entire bottom rolls on ALL shower walls to prevent any future problems. Replace it with "Concrete Tile Backer" . The backer comes 3ft x 5ft . When you attach it to the existing wall studs use only galvanized or stainless screws. When you replace the tiles use only mastic that is for WET AREAS. Also, I would be willing to bet the problem area is opposite the shower head. DO IT RIGHT/ DO IT ONCE