Interesting that your RealTracks instruments would play sometimes, but not always.
I found this thread because when I opened up a file made with BIAB 2008 (and now I'm on 2021 version), an intro chorus played fine, but on the repeated solo choruses, nothing but drums. (All RealTracks).
Had to copy the badly played choruses, delete them, double the first chorus (played ok), back to one time, then paste in the solo chorus change... basically, quasi-recreate the file. This is not the first time that BIAB behaved strangely on files made with the much older version, either.