I've got the same problem, and I see no solution on this forum, only complaints. Is there any solution available? I have to build a dual keyboard setup because of a Hammond simulation. So I put my old Keylab61-MKI as bottom manual, and my new Keylab-MKII as upper manual. Both sending midi through a iConnectMIDI model iCM-0101 midi hub to a Hammond module from Ferrofish (the B4000+). Both manuals work but sliding on the upper manual (MKII) mostly result in hanging notes where the MKI has no problems at all.
Can you enlighten me ?
To be honest, This makes this setup impossible for me to take on stage, and to be serious about making music with hardware gear from you.