Hi. You have more than one type of groundcover in your photos. The groundcover in the photo with the rock is mostly periwinkle (Vinca minor), which is the plant with simple leaves with smooth (complete) edges. However, in the lower righthand side of that photo and throughout the other one, you also have wintercreeper euonymus (Euonymus fortunei), which can be distinguished based on its serrated leaf margins. This page from the U. of Maryland has some good images of wintercreeper, and this page from the U. of North Carolina has lots of photos of periwinkle (along with a video) to help you distinguish the two. As far as I can tell, it is the wintercreeper that is dying back and not the periwinkle. This page from Clemson U. lists the common insect pests and diseases of wintercreeper. Nothing on that list matches what I’m seeing, which looks like relatively quick dieback of entire vines (as opposed to spots or scales on the leaves). However, the paragraph at the top of that page notes that members of the genus “do not tolerate waterlogged soil.” Given the relatively wet summer and sporadic heavy rains that some areas of Ohio have experienced recently, I wonder if it is possible that those are low, waterlogged spots and that the plants in those areas are dying from waterlogged soil? I think that is the most likely explanation, especially since the surrounding wintercreeper looks fine. If you want to know for certain (or at least get a second opinion), you could send a sample (preferably an entire plant, including the roots) to Ohio State University’s C. Wayne Ellett Plant and Pest Diagnostic Clinic. You can find instructions for mailing a sample here and for submitting a digital sample (photos) here. Both have a $20 fee.