emeraldsoul
Scook = Genius.
 
I have tracked it down to Equilibrium Mono, the VST 2 version. Kills any X3 project. Stereo Equilibrium of both VST2 and VST3 works fine.
 
I'm off to download the upgraded DMG Equilibrium . . . MANY THANKS to scook, dub, YouDon'tHave, and John. I'll report out my hopefully good results . . . great forum thanks . . . -Tom

Excellent!.  

I knew Jack. Jack was a friend of mine. Emeraldsoul, you are no Jack.
 
The DMG Equilibrium update solved it. VST3 64bit, works in mono and stereo, I have my X1 mixes back, thanks again!
 
-Tom

Yes I remember working with Dave Gamble to resolve this earlier this year. The issue was that the eq plugins expose multichannel audio outputs that are not presently supported via VST. This was actually causing a crash in SONAR. In X64 windows certain crashes get "swallowed up" by the OS and the net result is what you saw - random behavior lack of audio etc.
 
DMG worked around the issue on their end in an update and we have also added code to prevent this problem in SONAR.

Oh, that's excellent, good work on both your ends. Thanks - Sonar's a great DAW, which I married after I got divorced from Cubase VST5.   DMG Equilibrium is the only EQ that I routinely use for boosts without feeling like I'm tainting the audio. Great to have both playing nicely.