Why is the audio on some clips not playing...

The audio on clips that were recorded on an external Atomos recorder doesn't seem to be working in FCPX. What have I done wrong this time? The audio comes in as 4 mono tracks but they aren't playing. Why? I know that 1of the tracks has audio and the other are silent. Also - what is that merge type arrow at the front of the clip? I have never seen it before.

Any ideas what I am doing wrong?

Thanks in advance for any ideas.

here are screen shots of the clip...

A bit more information...

I know the audio on that channel is good quality. It plays well when in Premier. Possibly that's the issue? This time line was an edit in Premier then I used "send to X" to export to FCPX. Possibly that messed something up? I really don't understand why the little arrow merge icon is on the track - does it mean "mixed down"? How do I change that?

Best,
Noah