Webinar wouldn't transition from practice to live

We have used Webinars/practice sessions for a while and first had this issue Jan 4.  The practice session worked as expected. When "Start Webinar" was clicked waiting attendees got a loading graphic (based on reports) and were not admitted.  There were over 150 attendees waiting to get in and the Participants counters never rose above 0.

We were finally able to launch the webinar by ending the event for all, restarting it, connecting presenters, then going live.  Any idea what happened or potential solutions shy of ending the event entirely?