MuseScore 4.0.2 keeps forgetting my MIDI input

I use a mini keyboard for ease of note entry and have just moved from v3.6 to v4.0.2.

Note entry works (though there is quite a lag) and is fine while I am doing a session of note entry. When I go back into note entry mode, it sometimes works and sometimes not - when this is the case, the edit preferences I/O shows blank for MIDI input. When I click on the dropdown, my device is listed and I can select it again - this works for a while and then stops a few minutes later.

Given that I am able to work for hours on end with this device in MuseScore 3.6 (and have done since encountering this problem), I do not believe it to be a problem with the MIDI keyboard device.