Music audio cuts in and out but speaker audio doesn't

We're using Zoom to record and then post to YouTube our live worship services. We're using vMix software, controller, and soundboard to manage two cameras plus the Zoom desktop. For the past several weeks, the music audio (choir, congregational singing, organ, and piano) cuts in and out every few seconds. That does not happen with the spoken word. Any ideas on what may be causing the issue? We've tried settings for original sound both on and off as well as trying other settings such as Stereo Sound, noise suppression, echo cancellation, and so on. Nothing seems to fix the issue. Ideas!