We have some minor dents in our home. We applied a thin coat of drywall paste, waited for it to dry, sanded, and then applied two coats of paint. When standing at an angle perpendicular to the wall, we can see the round spots where the drywall was applied. It was sanded very well. Why is this happening? Would a primer have helped?
A good acrylic primer would have helped. It's possible the patches have absorbed the paint causing them to appear slightly duller.
Try applying another coat of paint to the patches. Use the same application method you used to paint the room. Example, if you rolled the walls use a roller to spot paint the patches. A "hotdog" weenie roller works great for this.