This patch of Aptenia was growing well, extending down a grassy bank, crushing the grass as it went. All of a sudden (it seems) a large part of it has died off. I have no idea why. Suggestions please.
Info: There are no dogs. There are a few small cats. The whole patch lost a lot of foliage over the cold winter, but it recovered OK - as you can see in the adjacent parts. I have not sprayed weedkiller nearby