I am wondering if this is a swamp white oak. The leaf margins look a bit more "wavy" to me than hornbeam leaves, which are finely serrated. Regardless, this looks like the work of an insect. I think it may be a type of webworm, but I will have to check in with some entomologist colleagues to be sure. If you have the tools to get up close to the tree canopy, you could prune out the affected branches/clusters of leaves and dispose of them.

At least one of your photos shows webbing on the brown leaves. This could be an indication that Eastern Tent Caterpillar (https://www.canr.msu.edu/resources/comparison_of_the_eastern_tent_caterpillar_forest_tent_caterpillar_and_gyps) or another tent-making caterpillar is present. If you're able to, I'd recommend pruning out the affected branches. If you can't prune these areas out, a bit more defoliation or browning could occur as the caterpillars grow.