Midi ii/o using portaudio fails erratically

I've got a PDP220 piano with usb2midi cable. I can play midi files to this using audacity but what should be straightforward in musescore is an unpredictable nightmare. So I go to prefs, select i/o (keyboard is on and plugged in) select MME as the api selrct Microsoft sound mapper -output as the device, Select USB2Midi cable as the input - ditto for output.
click on the din plu icon (yes I have checked that midi not input is checked on prefs) try playing notes - zilch
try playing a mscz file - it goes to the speakers
Return to the prefs page I find the midi output/input options are blank. try restarting all audio devices - still no options showing for midi output.
However on another occasion I have found there is a device option which shows 'Microsoft sound mapper input' selecting that and the usb2midi cable options allowed me to play through the piano/midi. Unfortunately if I then try a different piece of music it reverts to the former behaviour (midi options missing)
I've tried uninstalling usb2midi and reinstalling with latest driver - Midi plays fine through Sibelius and audacity. Does anyone have any suggestions for how to track this one down? (pls dont say use 'Jack' a) Jack is appallingly tricky software on Win 10 and b) It says on the Jack site that it does not work with 64bit software
I am running Musescore 64bit ver 3.5 .13.199
Oh yes I tried reverting to 'factory settings' all to no avail. apart from the missing 'devices' it seems the problem is it not retaining the midi in out settings - you can (if it chooses to appear) select 'MM USB2midi cable' for both midi in and out but apply that setting and close the dialog then next time you open up prefs it has disappeared and both entries are now blank - it seems closing preferences blanks them.
occasionally it seems it might be connected with the way in which musescore loads audio drives or plays midi from its ative files - if you play something with sibellius first there is a chance that musescore will play a mscz direct to the midi piano but after a while it reverts to speakers ARghhhh