This exact scenario happened to us as well on December 6th. After numerous contacts with support, I'm beginning to believe they have no idea what happened. Some key elements of this experience:
-Event shows as 0 attended on the dashboard and there is NO attendee report.
-The day after the event, support assured me the data would be there within 24 hrs of the end of the live event. It wasn't. For this reason, I deliberately delayed follow-up Emails with an estimated 1K of attendees that were supposed to get a certificate.
-Contacted support again on 12-8 and was now told the data would be there within 48 hrs. Attendees were starting to complain about no certificates. After asking support whether follow-up Emails would go out properly with the attendee data missing, I was assured the Emails would broadcast normally. This was a false statement. The Emails went out alright, only that attendees received "Sorry You Missed.." Emails. My inbox quickly flooded with angry Emails.
-It's now 12-14-22, more than a week after the affected broadcast and GoTo still has no answers, only conflicting opinions from their reps. Since I'm unable to resend certificate Emails, we created a recorded version of the event (with certificate) and advised attendees to join it so they can get their certificate that way. It's the only workaround we could think of in the absence of answers from GoTo.
