no Zoom Webinar Attendees in Salesforce after running a webinar

With Zoom-Salesforce Integration app installed, after running a Webinar, no Zoom Attendee or Zoom Link records were created.

This webinar had more than 400 registrations.

The attendee report in zoom has nearly 500 rows.

But zero attendee records, zero link records in Salesforce.

Why did this happen, and how can i make sure it doesn't happen again for my dozen or so upcoming webinars?