Google meet seems to break down mid session

I'm running a 2020 iMac using Monterey.

When I host a Google Meet session it starts fine for the first 30-40 minutes and then my audio output turns into crackle/robot voice. (As reported by everone on the line).

Switching to a different mic (iMac internal) then back to my proper mic seems to fix it, but I would realy like to understand why it happens and if it can be fixed.

I'm using Firefox as my browser. The mic and headphones seems to make no difference as I've changed them several times to no avail. My internet speed is 500 down 50 up and i'm connected via ethernet to the box.

Any ideas appreciated.

Sam