Wallpaper and Wallcoverings - Stripping old wallpaper to repaint

Hello,
we asked a "professionnal" to redecorate the rooms in our condo. He had to strip the old wall paper, prime and repaint.
The job was finihed last week and immediately we notice that the paint was flaking in many places. He obviously made a mistake. What do you think happened ?
Did he leave glue from the old wall paper on the drywalls, or didn't he wash them correctly, or
didn't he prime the drywalls, or didn't he let the drywall dry enough etc...
He agreed to fix it. What should he do ?
Prime all the walls again and then repaint or sand the flakes and then repaint.
I thank you for your advise.
Regards
Georges

Yes & Yes. He did one or more things wrong. Please understand my position. From what you say, there was/is still glue that wasn't washed off, primed over properly, and/or sanded well enough to eliminate these trouble spots. What needs to be done, depending on the seriousness and depth of these areas is to scrap and sand the flakley spots, dry spackle if necessary, and prime. Here's a freebie. Make sure the primer is a sealer/bonding primer and you can have it tinted to the same color as the paint you're using, which will save you having to double-coat these areas with paint, that is. After the tinted primer dries good, one coat of paint should cover well. Unfortunately, depending on the size of the area and type of paint, you may have to go from corner to corner to get a good finish. Sure hope this helps. Good Luck.