Hey folks.   Any ideas please?
I inserted a synth into a song.  To give it that synthie, pop feel i started tapping on a key on my midid controller keyboard pretty fast. I think the notes are 16ths.   I went into PRV just to manually move notes left or right etc as need be.    Basically when i expand PRV there is a note in every "box".   All good.  Or so i thought.
Finished the song..played it back and noticed a lot of those synth notes were not playing.  I put the synth track on solo and slowed the tempo right down and hit play.    Everywhere a note was silent (even though the was blue dot in the PRV box) i deleted the note and use the mouse to manually put the note back in.  But the problem persists.
Thank God i did a "save as" so Im trying to fix this problem with the song saved.   So i can goof around with this safely.
I deleted all of the midi notes and decided to start again using just one bar.  My plan was to get one bar right and then just copy paste.  But even on one bar Im still getting these silent notes.  Ive tried using event manager to select all notes and then going to the quantize tool    Even quantize didnt help.    I know the problem is not with the keyboard because even when using the mouse to manually put in notes this happens.     
I also tried using a different synth to eliminate that but the problem remains.  If i hold a key down and player longer notes it seems fine.   Very frustrating.  
 

Go to preferences - midi - playback and recording. Under "playback" increase the number in "prepare using ____ millisecond buffers". Set it really high and it should work. Bring it back down to record.

Nice one Steve.  That seems to have worked.   The default was only 125.   I found another article saying it should be up at like 500.  And one user had to raise it to 2K.    wow.
So you put it back for recording yes?
 

No need to use a different setting for recording. It is a playback buffer setting.

Agentcalm
Nice one Steve.  That seems to have worked.   The default was only 125.   I found another article saying it should be up at like 500.  And one user had to raise it to 2K.    wow.
So you put it back for recording yes?
 

To be honest I don't record much midi, usually program. Mine is set at 1000 and I never change it.
 
Scook, I had always assumed that if you were recording something along with a midi track that the midi playback buffer COULD have some effect on latency as you ARE playing back the midi track in order to play along with it. Is this a non-issue?

It is not an issue. A large MIDI playback buffer may feel like the transport start button is sluggish. Playback will not start until the MIDI playback buffer fills. The latency experienced when sending MIDI data from the controller and the results heard is the result of buffering by audio interface driver and plug-in delay compensation.

The setting also influence the delay between MIDI manipulation (f.e. changing parameters in MFX plug-ins on MIDI track) and resulting sound.
 
(Technologically) the setting comes from DX times, it should have no influence on VST based synth, but
(observation) practically it seems like triggering some bug in Sonar when hitting particular combination of ASIO buffer size and particular number. If  1000 does not work, 500 / 200 / 700 / etc. can help to prevent the bug happened.
 
MFX (and I guess Sonar internal processing) distinguish between "real time" MIDI which is delivered "as is", so as original MIDI events, and  "played from the track" MIDI which is processed using the buffer size specified in this setting and represented differently ("Note On" followed by "Note Off" events vs "Note + duration"). VST has no such separation, MIDI data are processed using audio quantization. F.e. for 44100Hz ASIO buffer 256, that is ~6ms. And so any "preparation" over 100ms in advance should not produce any troubles. But as we all could observe at least once, that is not the case.