Sounds like the shrub had a pretty rough winter and the stems dried out but the roots are generating new stems so all is still fine. Even though oakleaf hydrangeas are winter hardy to your zone, this can happen if environmental factors work just right.

Completely dead stems can now be pruned off to ground level. Partly dried out ones can be pruned from the top downwards in small increments; stop when you get to green or to the bottom.

Wildly fluctuating temperatures, fertilizing too much or fertilizing in/after July can have detrimental results as these things will keep the plant in growth mode when the plant should instead be going dormant. Not much you can do if Mother Nature keeps the temps going up and down but you could winter protect the shrubs in order to prevent the stems from dieing. I prefer to stop fertilizing by June, maintain 3-4" of mulch at all times and water the shrubs before a big drop in temperatures. If your winter is dry, this can also promote the death of stems. Watering during winter (provided your soil has not frozen) once a week or once every two weeks is the only solution to that.

I had a late start to winter more than 5 years ago when the highs stayed in the 70s thru December. Then winter suddenly arrived and with a vengance; temperatures dropped below freezing for a week. It did kill some of the stems but the majority survived. The problem was that almost all of those stems that survived had their flower buds killed. So I got only a handful of blooms.

pic fixed

thank you SO much for your advice and sharing your wisdom! i will do what you said. I am sure I contributed to this situation because I definitely fertilized july and august...maybe even into september? and thank you to the person who fixed my picture! i didn't know how to do that! :)

Interesting point about dormancy. I had an Alice that hung on longer with nice red fall color than any other plant in my yard last fall.

It completly died back with one tiny 1/2" sized leaf at the bottom. Unfortunately I didn't have the patience for it to rebound.

My Alice was 100% hardy during first year in ground, but the deer got all but one flower bud after a rainfall, before I had a chance to reapply Liquid Fence. You win some, lose some!