Any ideas what's wrong with this

Is that your neighbor's property on the other side of the chain link fence? They may have used weed killer.

Nope - seen this in my garden too It's strange because only a few stems of a cultivar wilt.

It's hard to say what could have caused this, but do remove the dead foliage, discard in the trash, and sterilize your clippers in between plants.

Did you push down on the soil near the dead stems to see if a critter (like a mole) had dug a run there?

I have actually had chipmunks repeatedly dig out a hole under a peony, despite me filling the hole several times over two years, and the peony - Do Tell - didn't wilt even one leaf I think the problem is at soil level and possibly it started in the Spring with a mild case of botrytris or something that weakened the stem/s. Later in the season high wind or heavy rain caused the stem to break either completely or partially. Just a guess.

I examined the space. No holes or any indication the space has been meddled with. I doubt the neighbors used any weed killer. They mow their lawn and that's the extent of their gardening. I removed the badly wilted stems and was left with one or two healthy stems. We've had insane amounts of rain lately. I guess I'll wait until next year and hope the plant itself is ok.

I'm going to bet it will look fabulous next year Peonies are exceptionally resilient to all kinds of 'injuries'. I have a critter (probably a rabbit) that taste tests everything along one path so has bitten off small peony seedling stems leaving some plants with no stems at all. Many weeks later there are new stems appearing