Missing Audio Track in Timeline

Greetings all!

We are having some issues with audio tracks in our project. Two tracks were recorded in camera on an Alexa Mini (on board mic and lav) but only one is showing up on the timeline (the on board mic). The project was assembled by somebody else, so I don't know what settings were used, but when I import the same media into a fresh project both tracks show up and I can hear them both in the source monitor and timeline (even though when I go to Modify-Audio Channels the set-up is the same: "Use File" and "Mono" with 5 tracks). Track Output Assignments is greyed out so I'm wondering if that has something to do with it? It's a large project and editing has begun so we can't start from scratch.

Any help or suggestions hugely appreciated!

Ashleigh