Community
Do you know if you've installed the latest update (Fusion 360 version 1.8.674)? This was released on Oct 14.
If so, did you recently install the update? Have you been working in offline mode at all?
I am not sure if the following suggestions are relevent to your system, but I'll throw them out there. Have you tried disabling Firewalls, anti-virus, or updating any proxy server setting in the preferences?
Have you submitted any crash error reports (CER's) that may be related to this?
Thanks,