I get it at times. Workaround I do is move the folders somewhere else in SkyDrive then wait a couple mins for the photo hub to sync. When I see the folders aren't there anymore, I place the folders back in the original location. When it syncs again, the thumbnails get back the cover photos. Kinda annoying though since I think I do this weekly. I could very much leave it as it is but sometimes I get to be oc and simply need to see the cover photos
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