Did you perform hard reset? Or soft reset where it only prompts the hub to connect to ST servers and download firmware? The hard reset would be a drastic step that is not a guarantee to resolve this issue.
A better method would be to power down your hub for several minutes. Remove the battery if it is a v2. And be patient, some report it may take a day or so before it reconnects. Also, try plugging directly into your router and change the dns settings to a public dns server temporarily.
It is frustrating - just be aware this issue requires patience.
