Premiere freeze when external monitor enabled in playback

Premiere v15.01 on MacOS Catalina 10.15.7.

On my system, Premiere reliably crashes if I open a project with my external monitor enabled for playback. I can launch Premiere and get to the startup screen, but opening any project thereafter causes the spinning pizza of death.

At first I thought it was corrupted preferences, since restarting with resetting preferences would cause it to go away, but I tracked it down to specifically when the two "Adobe Monitor" boxes are checked under Video Device in Playback (I don't know why there are two monitors listed there, but both boxes have to be checked in order for the monitor to work in playback).

I can, at present, start Premiere, confirm that those are unchecked, open the project, check them again, and everything works correctly, but this is kind of annoying.

Does this sound familiar to anyone?