I opened up AD2 loaded a kit , Loaded the step sequencer with a basic 4 /4 kick clipped grooved it , played it and missing notes , So I tried playing the kick via my keyboard , same process same results. Maybe user error. 

I opened up X3 works perfect. 
 
EDIT: works perfect on new projects , only happing on some projects made with X3
 

I saw something like this too - but haven't had any time to investigate further. I have a song in progress and I'm using Superior Drummer. When I opened the song in Platinum - it was missing random MIDI notes when playing back the drums. If I "adjusted" the note in any way, it played back OK.
 
Every time I closed the song and re-opened it. The same thing would happen - but it's random notes that get dropped. Even playing back a few times - different notes would drop, or maybe the same ones.
 
I just assumed a "gremlin" got in to the file - that may or may not have to do with starting in X3e and then opening in Platinum. I couldn't be bothered troubleshooting (it was late at night) and just bounced the drums in X3e.
 
I'm pretty sure it's fine with a file created in Platinum - so maybe not worth spending much time troubleshooting...

cool thanks.. I'm going to do more investigation on it..

Change prepare using to 999. default is 500.
I think it is under preferences - MIDI playback and recording. Not in front of Sonar now.
The AD2 samples are prob bigger hence more overhead.

microapp
Change prepare using to 999. default is 500.
I think it is under preferences - MIDI playback and recording. Not in front of Sonar now.
The AD2 samples are prob bigger hence more overhead.

perfecto ... I set my middi buffer to 500 and everything plays back perfect, it was at 250.. Thank you sir!!

dj,
Glad it worked. This drove me nuts .
I have mine at 999 w/o any problems. Many others have it at 999 as well.
If your problem re-occurs for a different project, just bump it up again.
 
Hey what buffer size do you run with the FW-1884 and the Q9550 ?
At 48Khz/24, I can get maybe 256 samples for recording. Once and a while 128.

Thanks for the tip microapp. I'm busy working midnight shifts this week - so not getting much "quality time" to play with SONAR - but I'll give it a try too.

microapp
Hey what buffer size do you run with the FW-1884 and the Q9550 ?
At 48Khz/24, I can get maybe 256 samples for recording. Once and a while 128.

I use my Fw-1884 only as a control surface now a days . I only needed 2 inputs and 2 outputs having issues after 8.5 . I ended up with the Roland Quad capture.

My problem is similar. I'm getting missing notes on AD2, but only when using a MIDI Humanizer plugin (it's a midi fx). I tried the solutions in this thread and I also tried upping MfxLookahead in TTSSEQ.ini, but to no avail. :(