It appears to be moisture in the wall. The way that paint popped out, looks like it has had water damage. However, it could also just be a quick coat of paint put on, so it looked better for a new renter, and there was no cleaning of the walls, or prepping. Looks like a lot has just been painted over, with no thought to appearance. There is no telling what was on the wall, that they just painted right over, to get it done, and the place ready to rent.

In pics 1-4 I see paint that isn't adhering to the wall... could be it was painted without cleaning or priming the wall first, could be that the wrong product was used, etc. In the 5th pic I see a really bad wall patch job... probably done using spackle or joint compound and then not smoothed properly before it was painted.

I think its poor prep and painting technique. I have the same thing in my house in rooms where we have no moisture intrusion or previous water damage. But I definitely didn't know as much about painting those rooms then, maybe I washed the walls (probably not) and definitely didn't use primer. I especially notice this on areas where I used modern paint to paint over surfaces last painted in 1960 and they're just not adhering correctly.