This is really odd.......I'll see if I can explain it properly.
Subsequent to a Windows 10 update, all sorts of things went tits up on my Sonar X3 Producer so I thought, "why not upgrade to Sonar Platinum" as I was planning to do that later this year anyway, mainly for the multi-mix function.
 
Anyway, having done the upgrade I had a few immediate issues which were all swiftly resolved by a support call to Cakewalk - cheers guys, you were brilliant, but I now find that Soft Synths and MIDI controlled external devices (Roland JV-1010) are randomly dropping half a tone during recording or playing. This occurs with two controllers - an Alesisi Q49 keyboard and a Roland GR-55 Guitar Synth (although not on the GR-55 audio obviously) as well as during playback of soft synth and MIDI controlled tracks. I assume from this that, as the problem is global, it rules out the MIDI controllers as cause and because it also occurs during playback of soft synth and MIDI controlled tracks that it must be something to do with the relationship between SONAR Platinum and Windows 10 (64-bit) Version 1607 build 14393.321.
 
Anybody had the same problem and if so got any ideas how to fix it?

I'm not much help here, but . . . I have never have any issue with my old Alexis QS6 and I don't have your guitar synth, but have forever used a Roland GR-30 and have found the Bend Range and/or Chromatic give me your type of problem.

"Dropping half a tone?"
 
 
Does that mean that the pitch of a note (or a portion of the note) is lowered by a half tone? If so does the next note occur on the correct pitch or do subsequent notes stay low until the next event? Does the MIDI (the actual note number as opposed to the audible pitch produced by your unspecified synthesizer) show up lower?
 
Does it mean that half of the duration of a note is not played? Or that some notes are not played?
 
Does it mean that... never mind. I have no idea what you are talking about. 
 
Why not start over and describe in some detail what is actually happening?

OK, bearing in mind I'm in no way technical, I play a note on the keyboard or guitar synth and everything is fine for a period of time. For example, I play an E, it registers on the piano roll as an E but after a while the audible note drops to an Eflat (along with all subsequent notes being half a tone lower audibly) while remaining true on the piano roll. No notes are dropping out and envelope is not affected. The period of time until things go awry can vary from as little as a couple of seconds to several minutes. Soft Synth and MIDI playback of my external JV1010 are also affected. If I kill the MIDI and reset the Audio engine it fixes the problem but only temporarily. All this happens without any use of tone or modulation wheels on the Q49 or by using the expression pedal on the GR-55. SPLAT is the latest version with all current updates.
 
That's about as much detail as I can give. I can see no further indications as to why this is happening.

So if the MIDI note number is not changing, and the perceived pitch is changing by a half tone lower, the most likely cause is that you are experiencing a change in the sampling rate from 48 kHz to 44.1 kHz. If so you should also have a slightly slower playing of the recording, but that may be harder to perceive. The fact that it changes unexpectedly suggests that another application on your computer is taking control  of the sampling rate of your interface so that the interface is using a different sampling rate than Sonar. 

Check the event list and see if you have a pitch bend controller event in there. That could explain things

For whatever the worth, I recently began hearing slightly out of tune sounds if I played one plugin on my upper controller and others on my lower controller.
 
After much investigation, it turns out that my faithful Axiom Pro 61 controller has started sending out pitch bend and mod wheel midi messages by the HUNDREDS, and this seems to occur over time with lots of different company's controllers - not just Axiom.
 
For ME, I have disabled both CC's so that when I play on that controller the sounds are now playing correctly - and the LONG term fix is to get one of the circuit boards replaced for that controller.
 
I don't know if anything from this post would apply to your situation - just thought I would share it as something else you could look at to see if it is involved.
 
Bob Bone

Whistlekiller
OK, bearing in mind I'm in no way technical, I play a note on the keyboard or guitar synth and everything is fine for a period of time. For example, I play an E, it registers on the piano roll as an E but after a while the audible note drops to an Eflat (along with all subsequent notes being half a tone lower audibly) while remaining true on the piano roll.

 
I'm assuming you're not stopping or starting, correct? In other words, the pitch drops during a period of continuous playback?
 

If I kill the MIDI and reset the Audio engine it fixes the problem but only temporarily.

 
This implies that SONAR receives something not in the file itself that causes the change. When you reset, SONAR reverts to whatever value is in the file.
 
Try this: Disconnect all MIDI controllers, whether via 5-pin DIN or USB. Play the song through from start to finish several times, then report back whether the problem persists or not.

When I read the title first thing comes to mind is a controller sending a pitch bend. This can happen as Bob has said even if you don't think you've moved it. They can go wonky.
Craig's advice on disconnecting all controlers is your best bet.
And if that  doesn't stop it then yes, look in your event list.
I doubt if it is a sample rate issue that's just not possible mid song without things crashing to a halt, and Sonar will warn you anyways when that happens.
 

Thank you for all your replies. It would appear to have nothing to do with other programs as there are none on here apart from Windows and Sonar. No pitch bends or other MIDI info apart from the note are being introduced (see previous reply). There is no slowing down of the track - I've checked this with an external stopwatch.
 
Both controllers have been disconnected and reconnected after a shutdown. It makes no difference.
 
Anderton.......it happens during recording and playback. Problem still persists.
 
Cactus: I agree it's not a sampling thing as it's too random. It'd either be right or wrong all the time if sampling were at fault.
 
Nothing untoward in the Event List!