We've had a few reports of this. It's Google's servers failing to connect, there isn't any action we can take directly, unfortunately. Google have deprecated their realtime API, https://developers.google.com/google-apps/realtime/overview, but maybe they are slipping on maintenance prior to the closure date. We have a replacement system in the work, but it's not quite ready yet. In the meantime, switching autosave off seems to help (it's not really autosave, it's a backup, your changes will still be saved).

UPDATE April 24, 2018:

We've filed a ticket with the Google realtime team at https://issuetracker.google.com/issues/78443417. Please star that issue to indicate the importance to Google and if you are technical, please detail any traffic to the realtime servers that receives an error response.