What is causing these screw pops?

[pulck]

I had a loft conversion done a few years ago. About a year later, I started getting screw pops along one edge of a bathroom wall. (The bathroom is at the rear of the dormer and this is the rear wall.)

Someone told me to scrape out the plaster over the affected areas, tighten the screws behind, and then fill and repaint. However, the screws wouldn’t tighten further, so I just filled over them.

About a year later, the screw pops have returned in the same area. I’ve now scraped them out again, but before repairing I’d like to understand the underlying cause.

What I've noticed is that the screws are very long - about 12cm - and have been driven in at an angle rather than straight. They've also been driven in quite deep, sometimes 1cm into the plaster. When I tried to drive in an 8cm drywall screw just below one of the existing ones, it did not connect with a stud.

Does this suggest the stud is somehow positioned oddly and that the boards weren't fitted properly?

Since the screws won't tighten, what should I do before refilling to stop the screw pops coming back?

Sorry for the dumb questions - I have little to no knowledge of plastering.

 

[foxhole]

If screws don’t tighten they allow movement which causes the plaster to pop .Cant see any plasterboard in pics ?

 

[pulck]

If screws don’t tighten they allow movement which causes the plaster to pop .Cant see any plasterboard in pics ?

I just assumed there was plasterboard but maybe not. If that's the case, what are these screws for?