small strip of wall next to the tub is molding
all these old houses have the same issue. the wall is 2" deeper than the tub and you cant put tiles there to prevent drywall damage.
you fix the drywall and it comes back. i am guessing the tub has a slight pitch and that's why the splashing water is rolling towards the outuside of the tub.
see the picture.
the corner guard is not helping, as you can see
anywhere to fix it? i have this issue on two houses.