Help Troubleshooting MIDI Dropout

I'm working on an orchestral piece using Sonar 8 Studio Edition and an older version of the EWQL Symphonic Orchestra.  In the very last measure, both the cellos and the contrabasses just disappear or drop out. 
 
Both instruments should be playing a sustained, three-beat note (dotted half-note).  But what happens is, the notes sound for a second at the beginning of the measure, and again at the end, with silence in between.
 
I thought at first that this might be caused by too many samples at once, even though no extra voices are added in the last measure.  I also thought it might have something to do with overlaping pitches -- a lot of voices resolve to E in the final cadence.
 
The dropout still occurs if I solo the two problem tracks, or if I mute all of the other tracks.  To reduce the processing load, I've tried archiving tracks, deleting tracks, and even deleting an instance of EWQL, but the dropout is still there.  I still think it might be a resource issue, but I haven't been able to nail it down.
 
I also tried re-sequencing the last few measures of the cello and bass parts, and copying the sequences into new MIDI tracks -- same problem.
 
I'm stumped.  Any ideas why this might be happening?  Any more troubleshooting suggestions?
 
As always, your help is greatly appreciated. 

But what happens is, the notes sound for a second at the beginning of the measure, and again at the end, with silence in between.

That can only be the synth audio dropping out, not MIDI. If the note starts, that means the note-on was sent and received. And if it were a "MIDI dropout", the sound would not restart without another note-on being sent. So it must be the audio output of the synth dropping out. To test this, try a different synth.

I don't know anything about EWQL, except that I see a fair number of posts about mysterious problems with it. I don't know if this is because it's so popular, or because its buggy.

A few things you might want to check.
    In PRV in the little purple box above the keyboard(show/hide midi events box)  click on show all continuous  events to see if there are any controller events on the track that might trigger this. 
    Check for note overlap.  Just click on one of the notes and drag it up or down to see if there is another note hidden behind it. 
    In EW I sometimes get strange behaviours when using the the legato function.  If it is on try the last measure with it unchecked to see if that is involved.
    In EW, if you are using multiple instruments in one instance of the plug in, if any of the tracks has a CC11 or CC7 that may be acting as a global function for all the instrument tracks.  For example if you recorded 1 of the instruments to fade out over the 1st measure of the ending it may be fading all the tracks in that instance.  Because EW doesn't show any visual fader response to the CC's it is sometimes harder to find the culprit causing the problem. 
    Sometimes deleting the offending note in the track and then inserting a note above or below where you want it and dragging it to the correct spot can solve some anomalies.

Well you can always create new tracks from scratch, then drag-drop the midi clips over. Then look at the Events List view to make sure the only thing you have in the MIDI clips are Note events.

Your welcome.  I discovered that one by accident and have no idea why it works and just replacing in the same spot does not.  Most definitely weird I know.
 Lorne

Under Preferences > MIDI > Playback and Recording, under Playback increase the MIDI Buffer Size. The default is too low for most systems, and this fix has been referenced numerous times in this forum as solving a bunch of baffling MIDI issues. Try 750 ms or even 1000 ms. This doesn't cause delays or latency issues.

Roger on the buffer size. This is embarrassing, but I always use the VST2 version because that's what I've been using for years...didn't realize there was a VST3 version until I read your post. The VST2 version has always worked fine for me, so try the VST2 version and see what happens (and I'll try the VST3 one and see if I experience the same issues). Also, you say you are evaluating it...is there a current demo version? I assume you have the latest SONAR demo that incorporates some of the VST3 handling improvements. but the z3tz+ 2 has also had several updates recently.
 
BTW many people have reported issues with Arturia soft synths running with VST3 and recommend using the VST2 version (which is what I use with them). FWIW I've had no problems with Steinberg, Waves, or iZotope synths running under VST3.