I think the thing to keep in mind here is RB is not Biab even though it has a lot of Biab functions. There's no problem in keeping both programs open as long as they both are not using ASIO. Just click back to Biab to audition styles.
In RB I will only highlight maybe 8 bars of an empty track and generate a part if it's a Real Track or Drums and if you want to hear the substyles pick a section that overlaps those. Much faster generation than doing the whole song. If it's a midi part it doesn't matter, midi generates quickly anyway. Another thing to keep in mind is the "generate all Biab tracks" command. This thread sounds like you are starting out with a Biab song and then expanding it to include new tracks below those Biab tracks. When you use that command only the blue Biab tracks get regenerated, not the other ones. If you don't want a Real Drum track to keep getting regenerated turn that off.

Bob

Biab/RB latest build, Win 11 Pro, Ryzen 5 5600 G, 512 Gig SSD, 16 Gigs Ram, Steinberg UR22 MkII, Roland Sonic Cell, Kurzweil PC3, Hammond SK1, Korg PA3XPro, Garritan JABB, Hypercanvas, Sampletank 3, more.