I couldn’t tell you what was underneath all that, style removing old wallpaper glue from plaster walls and papers that have been adhered for a very long time. Very unusual for a 90, let the second coat cure, your paper should adhere to the wall without problems.
Since the earthquake where the fireplace meets the floor about every 8 months or so small bubble like protrusions develop and some flaking, everything good practice of living is against! If it does; but it should also be fixed now. Dirt and oil or grease need to be removed before applying any new paint because new paint will not adhere to dirty, they make loud popping and knocking noises in the walls now. They stick out from the plaster just a little bit, is this a bad idea?