Please check the recent log messages (Admin Wrench → Administration → Reports → Recent log messages). Is there an error reported by Zoom?
If there is an API rate limit error, it indicates the learner registered multiple times, which will cause an issue. This can happen If the Zoom link is sent via a reminder email or signup broadcast, in addition to the Zoom course object being used. EthosCE uses the course object to protect registration limits and access before the webinar is ready to go live. If you would like learners to pre-register in advance on Zoom, then we recommend not using the Zoom course object and embedding the link in a course page.
Did the Zoom meeting go over the designated time set in EthosCE? We recommend adding some buffer time so that reporting within the API works appropriately even if the session goes over the designated time.
Do any reports in Zoom show attendance recorded?
In the Zoom API settings, is the correct webhook endpoint configured per our documentation?