Zoom webinar panelists can hear me (the host), but I can't hear them

I schedule monthly agent webinars and schedule them the same way every time.  Today, in my webinar, my agents could hear ME but I couldn't hear THEM.  I checked the settings on the webinar setup and the audio was checked "both" for telephone and computer audio for both me and my panelists.   An agent said there was a recent update to Zoom and maybe that is what is wrong?  I cannot see anything in the setup itself that could have caused this.