bill.
a few years back i had a similar midi prob , with extra stuff.
(i was useing a regular daw..pg powertraks.)
if i remember it was a roland i borrowed from a mate.
how i realised the prob was i used a little utility in powertraks
at the time called midimon.exe.
what you might try is essentially a dumb midi keyboard with no sounds.
they are about 80 buks now or so.
run a test etc. n see if you still get the same prob/anomolies.

one other thing ..a tip, sometimes if ya got other active devices on the usb bus,
sometimes they can "choke" the bus if they are very active communicating with
the pc. it doesnt sound like this is your case..but something to be aware of.

retired puter engr....powertracks on amd......NICE !
"what is the black art of audio engineering ?"
my silly songs...motagator.com/bmanning
see my tips in the tips section.