OK now I get it, the preview channel. I never even thought about it (DOH!).
OK one to add to my stupid list as well...
Glad you got it fixed...
 
Cheers...

Hehe... so can I chalk that up to a "background process" from #4 above??

Yeah, background process for sure.
 
Alex the plugin wasn't on the preview bus if that's what you mean it was just loaded into the project.  But Vienna Ensemble Pro Server isn't a "normal" plugin... it connects to another computer and loads and saves samples and plugins with your project via ethernet cable.  Obviously there is some issue there with X3 I have yet to research or work out because it seriously bogged down Sonar.  Not just the media browser but editing clips and a bunch of other things.
 
My brain didn't go there because I used it in 8.5 transparently in the background all the time, and X3 is so new to me I wasn't sure what normal behavior entails.

I should add: new computer, new OS, new sonar software.   With these bugs I run into I have no idea where to begin looking.  Clearly upgrading all three at once is a horrible horrible idea.  I was forced to, just in order to go from running Kontakt 5.2 to Kontakt 5.3.

Yep that's a good troubleshooting tip Mettelus, you were right to point it out twice.

Sampled orchestral libraries are like the "King Kong" of drive-intensive demand. How big is that library? Despite the speed of ethernet, you are including other piece-parts in that daisy chain, and I would be much more inclined to seek a solution that fits in the same box as the DAW. Will they fit on an SSD? However....
 
Even saying that... I am sort of curious why that didn't have isues on an older machine... seems almost like the server/client in the new system is not set up "properly." I have no clue how that plug-in works, but now that you mentioned the server part, the 15-20 seconds seems like a "server sync" issue?

Yes something is not set up correctly.... I am just so happy to be able to work after being down for a few weeks that I haven't looked into it yet.  See the thing is, nothing was loaded on the other end of that ethernet cable.  I had Vienna Ensemble Pro loaded into the project, which connects to another computer via ethernet, but on the other computer zero samples were loaded it was just an empty plugin.  So it's not the sample size but the plugin itself.
 
I actually have 7 external computers that do nothing but load samples.  6 of them communicate via Midi-Over-Lan and contain their own soundcards which sends the audio out to my mixers.  I never have any issues with these computers, they are rock solid.  But they are load-it-and-leave-it computers for me, I never touch them.
 
The 7th computer connects via Vienna Ensemble, which means all audio and midi is transported via ethernet and the audio is brought back into the main computer.  It doesn't have it's own sound card.  This is nice to have because any samples I load into that computer (Kontakt, Play, Omnisphere, etc) are saved and loaded with the sonar project and use zero memory on the host computer.  Obviously something is not working though.  And yes I used to run this way on 8.5 transparently.  As I said all the strain of the samples is on the external computer.  All Sonar is doing is sending midi and receiving audio.  But there's more... because the external computer syncs to the main host tempo... and also loads and saves with the project... so that's where something is causing issues with X3...

Could it be something as simple as the plug-in on the other computer not having samples loaded? SONAR may be allowing that plug-in to "verify sync" before SONAAR does its thing (hence the hang). Just a thought there, but at least you know that plug-in can do this to you!