RingCentral Meetings uses zoom.us engine but the local server runs on port 19424 instead.
I'm able to replicate the issue on it.
PoC: http://localhost:19424/launch?action=join&confno=3535353535
PoC: http://localhost:19424/launch?action=join&confno=3535353535
I was taken into Miguel's meeting, but since the host wasn't presented, it simply let me know it was waiting for him (It also had a friendly notice "Your video will turn ON automatically when the meeting starts".
I've changed my settings in Video > Meetings, just like in Zoom, to turn off my vid when joining. Also confirmed that the server is running on port 19424 (via terminal command 'lsof -i :19424').