This is a little bit technical, but: what's happening here is that the display is not updating because the note is already off by the time it needs to show it. So it's not stacking up messages (like on then off) but rather showing whatever message is ready to show when it has a chance. Both the on and the off message are being processed -- so if there are subcontrols, they'll do their thing in response -- but in many cases the on message fails to show because the off arrives before the display gets a chance to update.
This is how other software and even hardware (like NI Maschine) does its work: if it cannot update the display, that's ok, but it always puts all processing first.
That said, we could try tightening up the incoming message throttle and see if that helps performance. Are you on the beta team? Would you like to be?