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Yes, Ive used Zoom before. Ive often had similar problems to the OP, most of which were caused by the microphone automatically muting itself.

I always keep camera and mic off by default and then turn it on when I want / need to.
 
I haven't used the iPad app but I know in the Mac app there's an option to automatically adjust Mic level that I've seen cause some issues. Maybe try turning that off if it's an available setting.
 
Depending on who set it up there might still be the option to have all on mute at the beginning of the meeting as a host preference.
 
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