It sounds like a midi loop.
In DP check your patch thru?
On your controller make sure midi in and out are connected to in or out. I have screwed up on my Yamaha Montage and put thru to midi in on Midi Express xt. That crashed it every time.
Try filtering system exclusive on Midi interface or Motu DP etc. Sometimes controllers send multiple controller data out at same time.
Try recording a empty midi track on motu with nothing assigned and use controller while recording, then open in Dp10 event list and visually see whats recorded! Sometimes there is sysEX Binary code or a whole bunch of controller # 1 all on one beat or tick. This says loop!
In your instance of Vienna Ensemble pro open preferences, Then select MIDI tab. Then make sure your setup is correct and not looped. If you select a external controller in Vienna Ensemble Pro and DP and have patch thru on this can create problems.
It sounds like a midi LOOP! they crash stuff fast. Midi loops can happen in software and hardware, and plugins, so check you midi interface settings, set external controllers to ONLY transmit on Midi ch 1.
This is a good start to rule out stuff let me know how it turns out for you!
I am watching thread so i can help. I run DP10 and Dp11 and vienna and use Mod wheel on Yamaha Montage 88 to control dynamics and a Expression pedal Controller #11. Older VST patches use Controller 1 Mod Wheel, newer use Expression #11 and Breath #2 to control patches.
Cheers and good luck
Kind Regards
B