Multicam clips not revealing all the audio tracks

I’m working on a project to produce over 40 short videos. Each video will have a two person interview filmed on two cameras, a Sony NX5 with a stereo guide track, and a Sony Z150 with two audio tracks, one for each tie clip mic of interviewer and interviewee.

I’ve been successfully creating a multicam clip for each interview, then cutting between the pictures leaving the audio from the Z150 (the tieclips) untouched.  Then I “Expand the audio components” to alter the levels as each participant speaks.

Latterly I been having problems. Some of the multicam clips, on expanding the audio components, reveal only one track.  I check back to the original clip in the Inspector and all the tracks are there.

I’ve no idea what’s changed or what I’ve done wrong.  Any ideas would be welcome.