i put these settings to change style to chorus # 2 but it doesn't work.

Is there any chance that you previously exported the song as an Audio File (e.g. mp3 etc) before changing the style for chorus 2?

unfold the song then you have complete freedom to change styles at any point. its also easier to use tags and endings. at least that's what i've always done when i wanted a bit more flexibility.

The reason I ask this is because if there is an audio track available in the same folder with the same song name, then I understand that this can play instead/alongside the BiaB file.

I guess I'm just trying to identify the possible cause.

Just checking that your song wasn’t frozen. It appears it is not in the screen shot, but if the tracks were frozen you would not hear the change.

Good point, and yes, I thought that also, but there is no indication of frozen tracks, so it must be something else. Hope the O/P comes back with further information.

the curious case is that if I change the starting style _COOL_IT with another style then everything works !!
Fold or unfold nothing changes.

I have created new file.....nothing changes.

Biab2020 limit?

Update to the O/P: I reported it to PG Music, so hopefully they will provide some feedback.

To the O/P, it seems that the problem is related to half-time instruments in the style.

Please see this post, which hopefully answers your issue.