From the Obsidian Discord:
PSA: Our main server was taken down by a forced reboot at 2024-08-24 3AM EST / 12AM PST. When the account server was down, our services like Sync, Publish, and account functions like login or sign up were disrupted.
Normally our services would have immediately auto-restarted, however we made a mistake in the auto-restart configuration, which meant that it did not automatically restart. I was able to start it up again manually at 8AM EST. Everything is back to normal now.
I have since located the configuration issue and fixed it so if this happens again it would be down for at most a few seconds. Apologies for the inconvenience!