I'm not sure what has changed, but after having not used MusicBee for a while, when I used it today, it won't play through my external speakers, only the laptop speakers. My laptop is connected to a Plugable USB 3.0 docking station, and the speaker inputs are plugged into the dock. Other audio programs, such as VLC and Windows 10 Groove handle this well and play through the external speakers as expected.
I checked sound settings, and the Plugable device is listed as the default.
At first Windows would not recognize MusicBee as an app to use for AutoPlay, but I opened MusicBee as an admin, and then allowed it to be added to the context menu, and then it appeared in the list. But sound still does not play through the speakers.