Brown spots on wall after painting

Question

We’ve been having some trouble with brown spots on a (freshly) painted wall.

Background info:

1. Moved in a few months ago and had decorator repaint guest bedroom (Dulux primer then Leylands trade waterbased emulsion)
2. Brown spots and damp started to emerge in the corner of the room - this wall/arch faces the outside. Had a roofer treat the outside wall to make sure no water leaks through.
3. Treated stains on inside wall with Zinsser stain blocker spray. Stains are gone but stain blocker is visible.
4. Few hours after fully dried, a new coat of the water based emulsion was applied. Shortly after, brown spots started to emerge again? They appear randomly and not consistently, have attached some pictures.

Possible explanations that I have come up with:

1. Outside wall was treated poorly and root cause has not been fixed. Less likely in my opinion because it hasn’t rained in over a week.
2. Wall emulsion doesn’t react well with Zinsser stain blocker and causes paint bleed? Not sure how likely this is because the spots emerged at placed where I didn’t use the Zinsser.
3. Underlying plaster is damaged/wet/has mould?

Possible solution:

1. Repaint entire wall with non-permeable and stain blocking paint. Possibly the Zinsser spray was not enough.

Any thoughts, ideas and tips would be greatly appreciated. I am not sure how best to proceed or what the actual issue is.

Also note: I’m an amateur and not a professional.

Answer 1

I fixed this issue over a year ago and haven't had any problems since. The solution was actually fairly straight forward: instead of using a water-based stain cover I used an oil based one. Having tried multiple products, I think the main issue was really the water based paint and stain cover that I was using prior. Do not use the spray, it's useless in this situation.

If you can get access to Zinsser products get one of these. I don't remember the exact number of layers I've done but I think it was no more than 2. Even one might have been enough.