You mentioned above that you didn’t sand it as it was smooth enough…you could try sanding it before painting it again. Perhaps it’s just ‘glass’ smooth, and sanding it will give the paint a key.
Dig/scrape it off, fill scrapes with easy fill. allow to dry for an hour or so, and then sand it flat. Wall will be flat and smooth again I promise. Its easy to sand, absolulty brilliant stuff, same texture as plaster skim and when you paint over it, it will dissapear. I use it all the time.
As per this post…Easyfill is the best stuff for filling smoothing walls.
You can get a bag of it, with 5 individual sealed bags inside, all you do is put some water in a bucket, put a bag in a mix it. It’ll last 45 mins or so before it goes off. I used a mixer with my drill to mix it and it’s a doddle.
I used loads of it renovating our house, it applies easily (I preferred a 10″ wide taping knife to apply it). You can get it mostly smooth without sanding with a bit of practice, but it sands easily.
I skimmed a few walls and they look perfect.
The only downside is the dust gets everywhere…make sure you get a good mask.