I use BIAB 2016 PC version and don't know how that correlates to MAC but I created a 12 bar 'song' with your style and 2 bar 'end' button checked and a I,IV,V progression. It replicates your findings as follows:
with style A (blue marker) The last chord is a V at bar 11. Bar 12 is blank and End is I. continues for a bar and does not end abruptly but each instrument ends at different times with guitar 2 extending beyond the other instruments.
with style B (green marker) The same ending results as style A, just different musical notes.

Removing the ending and placing a hold at bar 12 (ie: c...) resulted in a uniform single strumming of all instruments with the stum fading. The results of using the hold were the same regardless of what chord or chords were placed in bar 11. They were also the same if bar 11 was blank.

With bar 12 having chord or chords without a hold, the ending was abrupt the same as your results.

Suggestions:

Place a hold on your last bar or
Generate an ending or
Add additional bars to the end and fade your outro.

Hope this helps.

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.