This is apart of an ongoing issue with the Meeting IDs, we have posted info here Developer impacting changes during COVID-19 and will follow up as soon as Engineering is able to resolve the issue.
Right Side - Meeting Host (after meeting created using REST API, start_url loaded in an iframe )
Left Side - Attendee joined the same meeting using Javascript Web SDK.
When the attendee joined using Web SDK, Meeting Host clicked on the “Admit” button to admit that attendee in meeting…
And this happened