To provide an additional data point, I also have this problem on my late-2014 Mac Mini. I have a two-monitor setup. My main monitor is running at 1920 x 1080, and the secondary is at 1600 x 1900.
Edit: Macos 11.3.1 (Big Sur)
Interesting. Thanks for the update - I'll pass it on to the development team.
*EDIT* Are you using BIAB 2020 build 423, or a different version?