we have an oak tree that is showing some signs of having issues. Not sure...
I sympathize with you on your oak tree -- our neighbors have a beautiful oak overhanging our yard which we have spent more money on than they ever have,
Diagnosing a tree's problems remotely can be a difficult proposition, and I often advise people that if the tree represents an important part of your landscape, you should consult a certified arborist. You can easily find one by using this link from the International Society of Arboriculture: http://www.treesaregood.org/findanarborist
Having said that, I can provide you with some information that can hep you begin a diagnosis yourself. First up is a 12-page diagnostic tool from the University of Illinois; it has some great pictures: https://web.extension.illinois.edu/plantclinic/downloads/Plant%20Clinic%20Report%20Oak%20LO.pdf. Another good fact sheet is from the University of Maryland: https://extension.umd.edu/hgic/topics/why-oak-trees-are-declining. Finally, our own Ohio State University Extension has produced this detailed page of information: https://ohioline.osu.edu/factsheet/plpath-tree-02.
From what I have read, your problem could be caused by any number of problems including oak wilt, anthracnose, or bacterial leaf scorch. Best to consult an arborist.
Best of luck.