Akai Keyboard direct MIDI to USB connection, no DAW

I have Vital installed (extremely awesome), got my Akai MPK 225 to “talk” to it with a direct USB / MIDI connection (no DAW at all), but when I key in notes on the Akai, the notes stay “frozen” on, until I turn them off with the computer keyboard. I have the Akai on “generic” MIDI setting . . .
I’m probably missing something simple . . . any thoughts from anyone are much appreciated

My guess would be slightly low voltage on USB power, are the lights on the Akai good and bright.
You could try :-

removing other USB connections.
use a midi monitor like MIDI-OX.
does another vsti synth work ?