This’ll take some explaining…
One MIDI track, one layer
Assign the track to play the layer - works
Now in the Layer assign the input to a VMidi channel.
Assign the track output to the same vMidi channel - works
Now go back to the Layer and try to assign input to the Track - it goes nc
Go back to the Track and you will see that it thinks it is assigned to the Layer but does not play.
Reassign the Track to nc and then to the Layer - works.
Go back to the Layer, can reassign input and then reassign to the Track as expected.
Also note that the MIDI input indicator becomes stuck on at some point.
I think this may explain the problem explained here MIDI track not playing layer