Have you had the stain on the bathroom ceiling by the bath fan?
It isn’t hard to fix! First remove the loose popcorn. Next, use some popcorn patch to fix the affected area. This can be purchase in spray or a tub. I use the tub because the spray can be a little messy. Finally, after popcorn patch is dry, paint the area. This kind of stain must be painted by a oil-based paint. Sometimes the stain doesn’t go away when using a latex based stain blocking paint. I keep a spray can of Sherwin-Williams ProBlock handy. It comes in a can as well.