I do have that track, because it works perfect in BIAB itself. I can hear it, mute, etc and no N/A. If I would not have that track, it would not work in BIAB itself.

The problem is only with the Reaper plugin for BIAB.

In Reaper I can hear it, mute, etc but it shows (!) N/A. First image. Double clicking results in the second image.

I have Reaper 5.99.

This must be a bug.