What maybe the cause of uneven areas

[Coastline]

I have spotted some uneven areas on my ceilings in diffreent rooms, as I unsure whether there are pre-exisiting (before the water damaged). I would like to know:

1. if it not water damaged, what may have causes these'non flat areas' on the ceilings,
2. as they seem too small to be from the joint?
3. whether there are ways to make them less obvious or flatter?

 

[sparkwright]

Hard to tell without being there.

Could have been water behind the paint.

Could be a plasterboard nail or screw that's missed the wood.

Could be a weak spot in the olasterboard.

Could be loose paint gradually blistering.

Could be bad plastering in the first place.

Could be lots of things.

As for a quick fix, it depends on whether it's just the paint bubbling, or the plaster.

If it's only the paint, you could try a syringe with glue, and squirt a tiny bit of glue into it, and gently roll over the area with a wallpaper seem roller.

But of course, you could end up causing further damage...

 

[Coastline]

Before the water damage the walls and ceilings were painted with matt paint.
Since the water damage the uneven surface was not noticeable (hence, I am unsure whether they were there before), and it was painted over with diamond egg shell brilliant white white on the ceiling and an off white color paint on the walls

I am puzzled as there is another ceiling which I can see it has a bubbled and had not been painted, so cannot decide whether it is the egg shell paint showing it more. I wonder whether sanding it down and then paint over with an off white matt paint will make the bubble less obvious.

 

[foxhole]

If it’s a bubble then sanding would reveal .