Hey Bernie, hows things? I think OP will benefit from any discussion of patching/priming.
Firstly, that light will be brutal for highlighting the slightest defects. Flat may not be your best choice for wear/tear, but it will be for camouflage. BIN would be an ideal primer/sealer for your situation. BIN has a sheen and it's possible that the compound will absorb some of that and you're seeing the slight flash, but that doesn't mean it will show through a finish, even a sheen. Is it just a flash or can you see a depression or raised area? I would suggest that before you go chasing something, try putting some test samples of finish on the worst of the areas to see if what you see now goes away with the flat. Paint doesn't fix things, it just hides them. You're playing tricks with light, and, if you can't see it, does it exist?
You may want to consider sinking a few drywall screws in some strategic areas. Sometimes, if the rock is not tight against the studs it will make patching impossible as the movement continually disturbs the patch. Keep us posted Bernie.