I am not familiar with MOTU interfaces, and have not experienced hanging notes for a long time, but there can be many reasons for this. E.g. poor cables can affect signal quality (both analog and digital can suffer from this).
Does the MIDI > Reset (in the Cubase menu) fix the problem when it the hung notes occur?
Some devices also have problems with MIDI running status
With Note Expression (VST3.5), individual notes contain their own set of controller data when played polyphonically.
VST Expression, Steinberg VST
Cakewalk Sonar X3
now supports VST3!