Are you 100% sure that no child or anything else dropped a hairbrush, the shower head, or anything else on it? Otherwise, it's just difficult to get through, I think.
We definitely haven't used the tub at all for the last 6-7 months. It's standing in a corner, nothing can fall on it or anything like that, so it's about 2.5 m away from everything else, like the sink, for example.
And our daughter is 13, she has never used the tub.
Something can fall on it, and then a piece chips off. Shower head, toy, hairdryer, wooden handle, glass jar... The damage looks like that. This kind of thing doesn't happen gradually over time.
I saw the spot today where the paint was peeling off just a little, like a bubble, and then I picked at it, that's why it looks worse now.
That may sound unbelievable, but it's impossible for anything to fall on it. The shower head, for example, hangs on the wall in such a way that I don't even have to remove it when washing my hair; I just turn the water on and off.
I really can't explain it at all. When the first paint chip happened, I also first thought that one of the three of us might have done something, but now, good 6 months later and absolutely no use of the tub, it happened again...
I will ask the general contractor/plumber... but thanks for your assessment!