Have you recently added media (in particular photos)?
There is an internal process that will crawl your photos and transcode them into formats suitable for your smartphones so that you can view them using WD Photos. It is a very low priority process, so it can take quite a bit of time to crawl through your photos.
yea… probably. Give it a few days to work through the photos. As I mentioned this proess is a low priority process (so as to not impact performance). I know that with my photo collection (30GB), it took over a week to transcode my files.