I tested muting the 2nd chorus and it works fine for me.
Here are the steps that worked for me for the first Chorus to play all instruments normally, the second Chorus to play only drums, and the third Chorus to play all instruments normally.
( in a 3 chorus song Bar 1 represents bar 1 chorus 1, bar 33 chorus 2 and bar 65 chorus 3.)

Select measure 1 on the Chord Sheet and set the # of Choruses to 3
Open Bar Settings
In the Box All Choruses open the drop down menu - Check that Bar 1 is selected in the Bar # box
select settings Chorus #2 Bar 1
Mute All instruments
Drums Return to Normal
select settings Chorus #3 Bar 1
All instruments Return to Normal
Generate and play and Chorus one should play normally. At bar 33( Chorus #2, Bar 1) only the drums should play. At bar 65 (Chorus #3, Bar 1) All instruments should play normally.

BIAB 2025:RB 2025, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.