I found this today and it worked!! I was having issues after swapping to a new PC. I tried uninstalling and reinstalling the app and game, a scan and fix, deleting cache files, deleting entire cached directories, and even sat on blizzard's tech support for an hour to see if they could help. (They were very nice. They just don't have access to game servers so we were stuck in the same boat.) After 2 days of trying to fix this, this video is what finally did it. Unfortunately it is a windows-specific fix, so if you're using another OS, I wish you the best of luck.