These tell-tale bubbles are usually due to a loss of adhesion in areas, and the subsequent lifting of the paint film from the underlying surface.
Applying solvent-based paint over a damp or wet surface.
Moisture seeping into the home through the exterior walls (less likely with water-based paint).
Exposure of the water-based paint film to high humidity or moisture shortly after the paint has dried, especially if the surface was not adequately prepared.
If the blisters do not extend all the way down to the base material, remove the blisters by scraping and sanding. Then repaint the surface with a quality acrylic water-based interior paint.
If the blisters do extend down to the base material, first locate and remove the source of moisture, if possible. Repair loose sealants and consider installing vents or exhaust fans. Finally, remove the blisters by scraping and sanding, followed by a coat of the appropriate primer. Finish it off with a top-coat of quality acrylic water-based interior paint.