Prime comes off on its own (foto)

[diy-diy]

While priming wall in the bathroom in some places prime doesn't stick up and comes off on its own, very few places in fact. Shall I re-do everything or just sand problematic places and prime it again? What's the best course of action (less work, better results)?

[HayZee518]

Use a manual paint scraper and remove as much as loose flaking paint as you can. feather edge sand the rough spots. wall must be dry - prime with a good oil based primer then finish paint.