I live in a condo that is approximately 25 years old. There were what looked to be nail pops in the ceiling in the main living area, master bedroom and master bath. There is only attic space above these areas. The nail pops were recently fixed with the protruding drywall being removed and new mud applied. The individual doing the repairs indicated that "nail pops" were actually screws. Shortly after being repaired a number of them resurfaced.

What can be causing this to happen? The unit should long be settled having been built in the late 90's.