I would check for the possibility of both, too much sun and-or mineral deficiency. The deficiency could be triggered by a pH problem so check that as well (it could be too acidic or not have enough nitrigen, for example). Plant nurseries sell kits that may help you check out both of these things. There is a soil pH kit and a kit that checks for too much or not enough nitrogen. They are not too accurate but you just need to know if things are out of kilter.

From the pictures though, it appears as if the leaves in direct contact with the sun are turning all yellow and that is what happened to one of my hydrangeas when the Crape Myrtle that provided shade had damage from a hail storm. Opportunistic fungal infections can then arise and discolor parts of the leaves. I added a makeshift structure to give shade. But test the soil too as a precaution.

Luis

Thanks Luis, I think it may be all 3, sun, deficienies, and fungal infections. I do use that Bayer Disease Control (not the all-in-one) on a regular basis.
I will do a soil test this fall though just to be sure.