Mixer window always crashes when opening it again after closing it

On Arch Linux build x86_64, MuseScore version (64-bit): 3.1.0., revision: e26f7c4. Qt version 5.12.4

I start MuseScore, open/create a score, and open the mixer window initially ok. But then if I close the mixer window and open it again, the mixer window fails to populate itself (the window is an empty transparent frame). MuseScore still functions (I can start/stop playback atleast), but the mixer window is inoperable. I can press the x in the corner to close the mixer window. Subsequent opening of the mixer window similarly fails.

Only console output is:

[e@librem ~]$ musescore 
warning: Environment variable QT_LOGGING_TO_CONSOLE is deprecated, use
QT_ASSUME_STDERR_HAS_CONSOLE and/or QT_FORCE_STDERR_LOGGING instead.
Attribute Qt::AA_ShareOpenGLContexts must be set before QCoreApplication is created.
QLayout: Attempting to add QLayout "" to Ms::Mixer "Mixer", which already has a layout