I think this is a bug, but when you’re playing a song using autopilot and you hit “Fill” on the BB, either though a button, or though MIDI, it start the whole part over again instead of just filling the measure.
The expectation is that hitting “Fill” would just do a fill in and continue, just as if you set the fill in autopilot itself. I can see with the non-autopilot parts that it also restarts a part on “Fill” (even on the BB1), and while I’m not sure that makes sense either, if a song is 80 bars long, then it needs to stay 80 bars long. Restarting a part at the beginning makes a mess for everybody.
This is not a bug this is how it was designed, to get a fill to play at an exact time without restarting the part you need to set it to play at that measure
That would be an odd design for an autopilot. That means if you’re playing a song and you accidently hit fill, or transition, etc, the BB2 will lose it place in the song. Good luck if you’re performing a song live or in a band.
When replicating a song, then the length of the song matters vs just playing independent parts manually.