5th October 2016, 13:56
It might be a caching issue.
Try going to ~/.cache/ and removing the activityswitcher_wallpaper_preview.kcache file and see if after a relogin it creates correct thumbnails again. (Maybe need to switch to the activities for it to refresh the cache)
Try going to ~/.cache/ and removing the activityswitcher_wallpaper_preview.kcache file and see if after a relogin it creates correct thumbnails again. (Maybe need to switch to the activities for it to refresh the cache)