Glad you found the .wav file button.

I am calling this a bug and have passed it on to the developers.

I am able to reproduce this strange behavior in seven steps.

1) Create a new song in BIAB
2) Use the Soloist Feature to add a RT (it will appear on the soloist track)
3) Generate and play all tracks.
4) Freeze the Soloist track
5) Save the file.

6) open the file in BIAB-VST
7) You will see that the Soloist track is now Midi. The rendered Audio for this track is from the midi. The RT on the soloist is gone.

BIAB – 2025, Reaper (current), i7-12700F Processor, 32GB DDR4-3200MHz RAM, 1TB WD Black NVMe SSD, 2TB WDC Blue SSD, 1TB WD Blue, 2 TB SK NVMe, 6 TB External, Motu Audio Express 6x6