Crackled emulsion patches

[RP66]

A few years ago, we had a decorator paint our kitchen wall, before he started, he needed to remove a dado which was fixed at waist height.

Over the years we have noticed the paint crackling in patches, exactly where the dado had been fitted, what is the best way to remedy this before I put another coat on the walls so that this problem will not arise again?

 

[Wayners]

Picture will help get answer.
May just need a primer before painting or fine filler.

 

[hants jobber]

it could be the filler cracking if so rubdown and refill, prime then paint.
or it could be the painter ever put on a prime coat, if so scrape off any loose paint refill, prime and paint.