No bigleaf hydragea requires full sun so you can ignore that....at best they might tolerate it but ideally grow and flower best with afternoon shade.

Have you been having cold winters? It could be the plant is experiencing winter dieback due to cold. And it is a pretty compact hydrangea as well....only gets to about half the size of most other macs.

I have Forever and Ever, Cityline Mars and Little Quick Fire in full sun, they do very well only I bought them in 3 gallon containers. Everlasting wasn't available in anything larger, I think I purchased it somewhere in a 1 or 2 quart pot. I know they tend to do better in shade but I remember the description saying this one required full sun. Had I put it in a shady area it may have helped and yes my winters are quite cold. At this rate I might just remove it. It did have 1 bloom last season.