Hi there - thanks for the update.
We are experiencing this same issue - I had spend some time trying to figure out what went wrong in the early hours of the morning, and stumbled across this post from Helen (before you replied). Luckily in our instance, disabling the SAML integration allowed some logins to work, however depending on how others are using SAML I would assume it would not have been as easy as that for them.
The status page when I was troubleshooting said that everything is operational, and in the History, it didn’t have anything about the SAML issue. Even checking now, it still says fully operational.
It might be worth updating the status page: https://status.auth0.com/