usbMIDI wierdness when controlling some VSTs as opposed to 5 pin MIDI

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Hi Everyone
This is a very strange one. Some of my VSTs respond perfectly to switch or button changes while using my diy teensy LC controller. Others will switch once and get stuck. The controller is sending 7F and 00 commands while toggling. My Arduino Nano controller using traditional 5 pin midi with the same VSTs behave perfectly while sending the same commands. While running MIDIOX the commands look perfect so I'm confused as to the different responses .My question is there something I'm missing ?
I can post code but that doesn't seem to be the issue
If it's not your code what would it be?

Teensy run many, many, many times faster than a Nano and so buttons need to be debounced more carefully.

Another possibility is not clearing the MIDI queue for incoming MIDI.

PJRC said:
MIDI controllers which only transmit data should be designed to read and ignore all incoming messages. If MIDI-OX or similar software is sending messages to Teensy, this simple code will prevent problems with USB buffers filling up with never-read messages.

// MIDI Controllers should discard incoming MIDI messages.
while ( {
// read & ignore incoming messages

That could explain only some 'getting stuck' if they are sending MIDI feedback and others are not.
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