On Monday, September 25, we detected an regression introduced in an upgrade to our infrastructure over the weekend.
The regression would have manifested as, for some BigBlueButton sessions, the instructor could start and enter the sessions, but students could not join. Under the hood, there was a race condition in the state of the live session where our infrastructure did not return the sessions as 'active', which is the criteria for front-ends - such as Moodle, Canvas, and Schoology - to show the Join button for students to join and enter.
We began receiving reports of issues early Monday morning and, after determining the underlying cause, we reverted the upgrade at around 11:00 AM ET. At that point, all subsequent sessions should have started/joined normally.
We've added additional checks to ensure this issue doesn't occur again, and we apologize for any disruptions this may have caused in sessions.