I had the same problem and had to change the MIDI playback buffer to 800 ms (as was suggested before)(it's in the  MIDI section and ander playback and recording.  It's listed as Playback -> Prepare Using --- Millisecond Buffers).  Seems high but it works.  It appears to be soundcard related.  I have a USB sound card that works fine but my laptop's internal soundcard has the problem.

Techniwizard

brundlefly


And your MIDI Prepare Using buffer is set to...?

I think part of the problem here is that X1 defaulted to 250ms where earlier versions defaulted to 500. 500 works for most environments. 250 does not work for many, including mine. The magic number below which I start having trouble is 259.

I haven't noticed any change from build to build of X1, but different Hardware/Synths/Projects seem to have different sensitivity to this setting, so it could be something changed with build 255 that pushed some over the threshold.

Tried messing with the buffers a bit with no change, then noticed the latency slider was set to 100 mS x 4 buffers = 400 mS. Set that way lower to 5 mS x 4 buffers = 20 mSec and that seemed to take care of it. Don't recall on what night of adult beverage consumption I ever set it that high but whatever works.
Thanks for the reply.

Replying late, but this is a good point; higher audio buffer settings require correspondingly higher MIDI buffers, which may explain why systems using onboard sound cards so often need a larger-than-default MIDI buffer.

Had similar problem in X1c.   Incredibly frustrating.  VST instruments not receiving recorded midi notes but received fine when I played the keyboard live with input echo on.   Increasing the Midi playback buffer seems to have worked for now, but it could be coincidence.    The reason I'm on this thread is to find the answer.   So far, seems to be working.

Sonar has become increasingly frustrating with more time spent on problem solving and workarounds instead of making music.  I was reminiscing with a friend about  the good old days of Cakewalk Pro Audio 9 which was fast and stable.  Capability has improved but productivity and stability have taken a nosedive.   I've been a user since Cakewalk V2, but really considering changing.  

Sorry... just venting.