You've posted this query multiple times without giving enough details to diagnose the problem. Please tell us your location (nearest city & state) so we know the soil type and weather. Have any lawn chemicals been used? Is drip irrigation in use?

We've now had 5 identical queries but no pictures, location or details. Repeatedly asking without adding further information will not get you any nearer a solution.

I am in Louisville, KY. No lawn chemicals have been used. I tried to post pictures but I could not get them to load. Varigated Lirope. Drip irrgaion is not used. I do keep an eye on the drness of the soil and water them as needed. I use a moisture guage.

Okay super... now we can start thinking...

Variegated liriope growing in sun should be a foolproof plant for you. So my guess is wet soil. Liriope is highly drought tolerant but it can decline/rot in wet soils. Look at the placement of the runty plants in respect to your downspouts or other drainage features. You've had a rainy spring and there may be wet spots in your yard,

Well, I have several yellow and white variegated liriope in heavy, wet clay in shade--it's doing great and has been for 3 years (hoping I'm not jinxing it now). We're actually zone 6B/7A.