Comment from the C3 Community Discord (it looks like the issue is still persisting though at least on my side with regards to accessing forum, etc.) It does feel like there should be some kind of back up for at least sign in though (even with offline mode, sometimes I move to a different machine or new VM and I need to login in again.)
Website issues should be resolved, think was a combination of a) Azure network issue (causing connectivity problems to Redis) and b) degradation of performance from rollout of arcade caused by increased visitor traffic (significant).
The Azure network problem seems to of resolved, and we're adding extra capacity and have made a few changes on the VM's to improve performance significantly.
Everything should be OK now.
We've planned for these sorts of events with regards to access to C3, if you had it available in offline mode it should of been able to run with all features without issue.