How to stop (seal?) bubbling paint

[PT1984]

Currently making my way round the late 70s house we moved into last March. Every single wall is wallpapered. All outer walls are double skin brick with plaster. Internal walls are plasterboard.

It’s these Im having the issue with. They are painted straight on to the skim. Nothing unusual. What didn’t cone off with the wallpaper isn't budging so it’s received a good few sugar soap washes. A light sand, and a coat of Zinsser Peel Stop.

On the other two rooms Iv had paint bubbling in a few areas when the emulsion is rolled on.

Is there anything I can do with this one to stop that happening? Was thinking Zinsser 123?

[Slagathore]

Wouldn't the peel-stop do the same thing - seal the surface?

Sounds like the emulsion is reacting with something? So might need a bit more of a thorough clean/degrease of that area?

[OutInTheShed]

I had a couple of walls where the old paint seemed to soften when painted over, so the roller picked bits off, and some bits peeled.
I found hot water softened the old paint, so it came off with a wide sharp scraper.

[wolfracesonic]

This seems to cover your issues Peel Stop vs Gardz

[PT1984]

Im still a little lost. I have solved the first problem
of possible flaky paint edges with the Peel Stop. When I applied the peel stop I did see some localised paint bubbling. So should I just go over the whole wall with Gardz?

[Craikeybaby]

Gardz was my first thought. We used it in my son's room at the back end of last year, and it hasn't bubbled. Although after all of the effort, we would have rather just had the room skimmed.