Garage band 11 - Korg M1 legacy plug in works as a synth but will not work with a midi file

Loaded the new Korg legacy M1 plug in. This works with a usb keyboard in garageband.

Then loaded a midi file and assigned same plug in to each track. This is where it all goes wrong.

Track plays but no sound. Assigned apple sounds to tracks and it worked.

So the plug in works as a synth in the application but not assigned to a running midi track.

??