Name: Jessie Worsham Stockbridge, GA (Zone 8a) Northwest Georgia Daylily Society
This might just be a normal part of aging for this plant. Maybe it's time to propagate some new ones? Here's an article that might help. https://needlesandleaves.squar...
I know these plants need a lot of light, but indirect light is typically best; however, someone closer to your growing zone may be able to provide better information.