Having looked at the photo's there are a couple of things that puzzle me (1) why have you battened the walls in the first place, and not just float and set them?
(2) have you go some sort of membrane on the battens before the plasterboard? any way looks like a poor plastering job to me a good plasterer would have dealt with the joints as he went , meaning that as the plasterer starts to set , laying the joint in with the front of his trowel, i can also see other defects like screw holes and misses, the joint on the board directly in front of you looks like he may have caught the scrim with his trowel and pulled it away at some stage of the set and done a poor job of trying to repair it, i also think it has been skimped one coated plaster or to thin, and all that dose is cause you grief when you get little problems like joints showing through. there are two options to remedy the problem (1) is to get a decorator to caulk out the walls (2) get your plasterer back to do a re skim but properly this time.