I've done some more work on this. IMO it has nothing to do with VEP but is a Kontakt issue (or Kontakt plus Cubase issue - I'm on Cubase 6.0.7). It is really only a problem with complex patches, or for those of us with large templates where the effect is exaggerated.
I've finally come up with a simple repro that anyone who owns NI Komplete can test. I'd love to hear if you can reproduce this in your host.
Firstly, set your soundcard buffer as low as it will go to exaggerate the effect but certainly no higher than 256.
Here is the repro (in Cubase for PC):
1- Load up Cubase
2- Open a new empty project
3- Open up the tempo track (Control-T)
4- Draw in a long tempo ramp over several bars (make sure the insert curve dropdown is set to 'ramp' and not 'jump')
3- hit F11 and load up an instance of Kontakt
4- load up 16 channels of the patch 'Scarbee Clavinet - Full.nki' from the Scarbee Vintage Keys library which is part of Komplete (I chose this patch because of it's complexity and because it is part of NI's Komplete. There are plenty of other patches from 3rd party libraries that are equally complex and demonstrate the same effect - several of the 'combined' patches from Spitfire's Sable library come to mind)
5- hit F12 to see the 'VST Performance Meter'
6- Ensure that Kontakt is syncing to the host tempo by clicking the 'Master' tab (to the right of the 'Browse' tab) at the top of Kontakt, and checking the 'Ext' button is lit yellow
7- Move the transport to just prior to the first bar of the tempo ramp and push play
8- watch the ASIO 'meter' go ballistic when it hits the tempo ramp. (Note, that nothing is actually playing)
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9- Switch off Kontakt's 'sync to host tempo' by clicking the 'Ext' button off
10- watch the ASIO meter drop down to almost zero
The lower the soundcard buffer is or the greater the number of complex patches there are in your template, the more exaggerated the ASIO spiking. For those of us working in film and tv this issue is critical. Avoiding tempo ramps and relying on tempo jumps reduces the frequency of the spikes / crackles / pops but doesn't eliminate the problem. Simple patches with few groups/zones and little to no scripting aren't affected, only complex patches like the Scarbee clavinet patch but there are plenty of others. Even if the patch is only moderately complex the culmative effect of many such patches (particularly if you are using Kontakt banks) adds up across a larger template..
I've left a support ticket with NI
Brett