Shared audio cutting out for participants

[Medieval]

Hi. I am having a strange issue and would appreciate any response. Whenever participants speak, they lose the audio I am sharing as host. The only way to solve this is to change my speaker (input) to my microphone, at which point I then cannot hear them - but it does stop the music from dropping out for them. I have tried every possible setting and have reproduced this on a number of computers, so it seems to be a Zoom problem. We never had this issue until a few weeks ago. Thanks.