Hi @ch-nakamura,
Thanks for reaching out about this. Generally speaking,you’re correct in that we do not recommend embedding any Zoom resources in an iFrame, which is likely where this issue is stemming from.
However, I found this Salesforce forum resource that I think could be helpful for you:
https://developer.salesforce.com/forums/?id=9062I000000Qz4DQAS
I hope this helps—let me know if you continue to have issues, though!
Best,
Will