I GOT IT!  It has something to do with the latency compensation and FabFilter plugins.  I had them set for high latency linear phase, switched them back to zero latency and BAM.  Playback is normal again.  What the hell?  I've never had this happen before.  It makes sense because this all happened post mix.  After I added the plugins.  So, if anyone knows, how do you mitigate this behavior?  How can I run this EQ plug linear phase without it dropping out my midi playback?  This is MADNESS!

What's your MIDI Prepare Using Buffer setting? should be at least 500ms, and maybe higher with the high latency plugins. Some users have reported needing to set a larger MIDI buffer in Platinum than they did in X3. 

Hey Brundle!  There's a name I know from reading these forums for 6 years or so lol.  Thanks for chiming in.  YES, I think you hit the nail on the head here.  I instantly thought of a buffer issue somewhere.  I believe I am using 250ms right now, which is default I believe.  I will bump that to 500ms and see if it resolves it completely.  Is that a global buffer setting or project specific?  I seem to remember it as a global.  Another note.  I started playback with all plugs disabled, and linear phase on in the FabFilter ProQ.  As I enabled the first, playback was ok.  Enabled second, I got half the midi notes.  By the time I enabled the third EQ, midi was gone lol.  So the introduction of this latency little by little was indeed interesting.  I will try the buffer setting.  :)

Oh, and I am using X3, so I'm not in the same boat as the Platinum issue you are referring to.
 

Brundlefly.  You win teh interwebs.  700ms was the answer.  Now, is there any consequence, or dependancies, on this value?  CPU cycles?  If there is one thing in SONAR that has always boggled my mind, it's all of the buffer settings.  ASIO buffers....I get that.  But this buffer for example, never have needed to touch it.  Also, those read / write caching buffers.  Does anyone actually use that?  Again, big thanks.  I can move on to more important projects now.  :)

Looks like mine is a different issue so I'll do some digging to isolate whether its just AD2 and if it is still working on Sonar X. It's only the 5th issue I've encountered and I did at last get DPro installed fully installed yesterday after 8th attempt since the update so moving in right direction albeit slowly.

Glad to help Yes, it's Global. X1 lowered the default to 250ms, and a lot of systems (including mine) don't do well with the buffer that low. The old default of 500 works well for almost everything. Going a little higher as you did shouldn't cause any problems.