https://hgic.clemson.edu/factsheet/daylily-diseases-insect-pests/

Hemerocallis fulva should be rejuvenated after growing in the same spot for several years. The healthy looking ditch lilies that are naturalized are continuously growing into fresh soil. The roots become so thick and tangled that the plants can't take up enough nutrients.

so dig, separate, & replant?

you can see the dich lilies in the background. i have similar looking lilies lining beds along the curb. they're all doing well. the only place that i've had problems before is a 30" swath along my driveway that is close to a row of pin oaks. nothing thrives along that strip. too much competition for water with the trees. water rates prevent watering. i gave up my 25x50' vegetable patch cuz i couldn't afford to water it. the sewer bills rates are tied to water consumption so it's a double whammy. if i was 30 years younger i'd drill a well for outdoor use.

Rejuvenating instructions. I spent years trying to get rid of my ditch lilies. Digging pieces of them out will free up the old rootball and stimulate new growth.https://www.google.com/search?q=how+to+rejuvenate+hemerocallis+fulvs&oq=how+to+rejuvenate+hemerocallis+fulvs&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIJCAEQIRgKGKABMgkIAhAhGAoYoAEyCQgDECEYChigATIJCAQQIRgKGKABMgkIBRAhGAoYoAEyBwgGECEYqwIyBwgHECEYqwIyBwgIECEYqwLSAQkyNTU1MGowajeoAhCwAgHxBeqNRuxKEtsc8QXqjUbsShLbHA&client=ms-android-verizon&sourceid=chrome-mobile&ie=UTF-8#lfId=ChxjMe