If that uneven texture in the first photo is paint lifting up, then I don't believe it was caused by a missed area of mist coat. A severe reaction like that is more likely to be surface contamination under the paint or something wiped onto the wall after painting.
It's interesting that the problem occurs on both adjacent faces. Maybe there is something happening on the other side or the inside of the wall.
- Plaster still damp when painted
- Water leak
- Wax or oil on the plaster, check if water spray soaks in or beads up
I've had success cleaning off light surface wax/oil with white spirit followed by methelated spirit.
After fixing the source I would be thinking about a light sanding then sealing it with a couple of coats of shellac primer such as Zinsser BIN. Smooth any remaining unevenness with fine surface filler, light sand and then paint.