Hi Ed

Well I have just done 4 recordings using my Clavinova as the input keyboard
On to the melody track / ch while using an all mid style. Just to make sure there was plenty of midi activity going on. I also set my midi output from the style to play though the Clav while recording my keys into BIAB no dreaded latency this way.
So I was using the Yamaha midi driver both for input and output and sending nothing to the BIAB dxi no tick in box use vst /dxi
All notes sent from the Clav including LH chords AND Melody notes were recorded cleanly no stuck notes

I also tried from my impulse 61 controller keyboard using a dxi to handle the midi data. This also worked flawlessly no stuck notes.

Not that this help you only to say the Yamaha driver and BIAB seem to agree
May well be that the pc is busy as others have said.
I will keep thinking on this one.

BIAB2021 UltraPlus,AsusN55S1Tbssd, W10/64,Akai EIEpro
Yamaha CVP405,SquireStrat, CoolsoftVMidSynth
Novatation Impulse61 Ctr kbd, Cwalk blab Kontakt

http://mikesmusic.byethost16.com/