you have removed or scraped away the brown rock paper. without this backer or paper, the adhearance of other material intended to stick is compromised.
I would give up on your sanding, scraping, and hard labor and have the walls re floated or skim coated slightly to get back to a smooth proper finish. Then you can texture, prime/paint, wallpaper or whatever.
If any areas have large sections of brown paper removed, this should be addressed.