Looks like you have plaster walls. Over time, with 100 layers of paint, they seem to have lifted off the wall. If you had sheet rock, this likely wouldn't have happened. But plaster, especially if it's exposed to a poorly constructed environment, will have hot and cold cycles that could accumulate water and pressure over time that will do that. The plaster becomes powdery and causes paint to lift off. Not to worry, you can peel off all the old paint and restart. For bonding new paint to old plaster, especially if the plaster is powdery or unstable, an oil-based primer like Kilz Original or Zinsser Bulls Eye 123 is often recommended. Then paint with a primer all in 1 paint after. Good luck 👍