Audio works in meetings, but I cannot hear it in the video playback.

Hello, I am a teacher using zoom for class instructions.  I have used it for 2 years now without any issues.  Now all of a sudden I cannot hear any sound when playing back a recorded zoom session with my classes.   All audio has been checked, mics checked, speakers checked, etc.  Volume is up in all required areas.  I am baffled.  My students hear me just fine during the zoom meeting.  I can hear them fine as well.  But when I open the recording to play it back, nothing.  No sound.  Has anyone else had this situation happen, and if so do you have any suggestions?  Thanks!