NI Synths - no sound until X3 restart

This is a problem I've had since X1:  out of the blue, or so it seems, while editing in PRV, I'll press play and instead of the notes sounding, I just get a sort of soft transient sound for each not, like a muffled very short bass note almost.  The only fix is to close X3 all together and re-open the project.  But often it just happens again after a few edits.
 
I've messed with the MIDI buffer(?) size, but that doesn't do anything.  Any other settings I should try?
 
I don't believe this has happened with non-NI synths, and it definitely has not happened with any CW.
 
Running 64-bit W8.

Tree, can you test something for me please? When you do what you mentioned, are you using simple instrument tracks? You know, the ones that have midi and audio all in one track? If you are, try doing it the old way. Create a midi track, then create a blank audio track and put your VSTi in the effects bin of the audio track. Connect the midi track output to the synth you inserted on the audio track, set up your midi in and channel....then record something and work in PRV. See if the problem happens to you again.
 
This to me doesn't sound like a midi buffer issue. The midi buffer thing *usually* bites you when you hear note drop outs at random. Meaning, in one pass you may not hear a snare drum....if you stop at that point and press play again, the snare will play.
 
What you're experiencing sounds like the issues I've had with simple instrument tracks. I've had all sorts of weird things happen with them. Note semi-mutes, distortion, pieces of notes that sounded like truncated samples....stuff like that. The only difference with my issues compared to yours is, my stuff wouldn't happen until I saved a project and then reopened Sonar. 
 
For example, create SIT using say Kontakt, record, edit, everything is working as expected. Save the project, close Sonar down, wait a day or even if I just re-open the project and that synth would sound like the samples were half muted or truncated. I'd re-load the patch and that would fix the problem every time. Save and close the project, open it again, it would be back. This happened religiously with NI synths only. I reported the issue but from what I was told, only me and one other user had experienced this so it sort of faded away.
 
From that point on I have always used 2 tracks (one midi, one audio with my VSTi in the audio FX bin instead of SIT because it never gives me any issues or artifacts.) I don't know if this was something in the NI synths or with Sonar. But I had this issue in X1 and X2. I've not tried it for X3 though.
 
Anyway, I don't know if this is your problem or *a* problem at all. I just wanted to share that I too had experienced some of this with NI synths and switching from SIT fixed me. It's worth a try to see if it does anything for you. If it fixes you, it may be a bug that would be worth reporting. My worst offender for this was Kontakt 5.2 with the latest version of Alicia's Keys.
 
-Danny