iPhone 12 External Microphone for Instagram Live Rooms

I have an iPhone 12 and have connected an external microphone to it using a USB to Lightning cable that's connected to an audio interface. The external mic works when recording using the built in Camera app and it also works for Instagram Live, up until I add a guest to the live room. As soon as I add a guest, it switches to the phone's built-in microphone.

Can anyone replicate this? I haven't been able to find any posts on the Internet about it. This might be a question for an Instagram community forum, but I can't find one. Any suggestions would be appreciated.