This looks like heat/sun damage to me. It happens here, and I think I'm now considered in Zone 8a in my drier part of Texas. Shade will prevent some of it, but the plants seem to go into an inactive period after they bloom and the temperatures start rising. A lot of the foliage starts doing what I see in your photos. After a rest period, mine start growing again and usually by early fall they look good. Then some (those that are most inclined to go dormant) do it again because of the cooling weather as it approaches winter. It's been a remarkably wet and cool season here this year, but I noticed this morning that a couple that are almost done blooming have foliage die-back showing. It might be they aren't getting enough water. In my experience daylilies like water and it's pretty hard to give them too much, IMO. I have a few growing in those plastic pots that I just leave sitting in a rubber tub with water. They seem to like that.
