And when you play the song can you confirm that in the first chorus, only chords play for 1 to 32 bars (measures) and then chords and melody plays from bars 33 to 64, then when it repeats (what BiaB calls the 2nd chorus) the melody now plays from chorus 2, measure 1 ?

Check in the same folder that the song has been saved in, that there is not a corresponding audio file (e.g. xyz.wav) with the exact same name as the song (e.g. xyz.mgu). If so, delete / rename the audio file, restart BiaB, open the song again and see if the results differ.

BIAB & RB2025 Win.(Audiophile), Sonar Platinum, Cakewalk by Bandlab, Izotope Prod.Bundle, Roland RD-1000, Synthogy Ivory, Kontakt, Focusrite 18i20, KetronSD2, NS40M Monitors, Pioneer Active Monitors, AKG K271 Studio H'phones