Problems exporting from Audition through Media Encoder

Hi, I've been using Audition on a Mac with Catalina 10.15.4. Some multi tracks that I export through media enconder end up with only one channel being heard. But it depends, some more complex multi track sessions export just fine.

The screenshot I've attached here is what comes up when I select to export through media encoder. I believe the problem is with the Routing Options. I try and change it but it'll just switch to the other channel and I'm unable to select both channels.

This only happens when I select to export through media encoder. Any help will be appreciated!