"Under heavy CPU load" stands out in the OP to me. The audio engine needs to think/process/sync the outgoing data stream, so I will see a noticeable delay with a heavily laden project (like half a second). If SONAR has not responded to the first hit, it is definitely possible to queue the second, so the "start/stop" behavior would occur.
 
How long is it from hitting the space bar until the transport starts? Another option is to increase ASIO buffers to reduce the CPU hit (but this will not bring back "instantaneous").

The easy test would be to temporarily bypass all effects ('E') and hit play again.
 
If it's instantaneous then it's not your keyboard

Bristol_Jonesey
The easy test would be to temporarily bypass all effects ('E') and hit play again.
 
If it's instantaneous then it's not your keyboard

I would add to that... temporarily archive any tracks that have a ton of takes/splits/edits in them.

> and sometimes Sonar reads the consecutive key stokes and decides to stop and restart
It won't be the keyboard itself as clearly the keystokes are being buffered.
 
Otherwise this issue could almost be anything,...
 
Update your chipset drivers from Intel driver update site, and motherboard bios from your manufacturer I suggest, and run Windows update. Update your interface firmware and drivers as well...
 
Still an issue afterwards?
 
Download a copy of process monitor and process explorer and attempt to diagnose the issue.

So, I find this happening quite a bit to me as well.   It appears if I do a CNTL S (Save) the project, it clears up the delay and non responsiveness of the SPACE BAR.
 
This doesn't fix it all the time but most times it does.  I find it quite strange myself but this has been going on for years, it started so long ago, I don't remember what version change made me notice.
 
If there is another fix for this, I too would be very interested.
 
Thanks,
Jim

jimkleban
If there is another fix for this, I too would be very interested.

 
Why not try what I suggested? Some feedback would be good...
Cheers...

Back to the CPU load, what is causing the high load? Can anything be disabled? Background processes? What would cause a high CPU load in Sonar if it is not in playback or record mode?

DRanck
Back to the CPU load, what is causing the high load? Can anything be disabled? Background processes? What would cause a high CPU load in Sonar if it is not in playback or record mode?

As I stated, download a copy of process monitor and process explorer.
 
Here are the links if you like:
https://technet.microsoft.com/en-us/library/bb896645.aspx
 
https://technet.microsoft.com/en-gb/sysinternals/bb896653.aspx
 
You should be able to google plenty of articles on PC optimization.
 
Cheers :)

OK...  I don't think this is my firmware or driver issue... this has happened over more than one computer (actually 3 all together)... i do a new build about every 2 years... just did one this JANUARY/FEBRUARY....  the symptoms and the problem has been consistent over all the builds over the last few years.
 
The saving project "work around" fixes it most of the time and it usually happens after some heavy PRV editing sessions (I think the UNDO buffer gets very large and the save project clears it out).  But what do I know, I am only speculating.
 
Jim

jimkleban
OK...  I don't think this is my firmware or driver issue... this has happened over more than one computer (actually 3 all together)... i do a new build about every 2 years... just did one this JANUARY/FEBRUARY....  the symptoms and the problem has been consistent over all the builds over the last few years.

 
Glad to know I am not the only one experiencing this!! I haven't tested if the save improves this behavior but yes sometimes it works correctly even under a heavy load.
My project has over 60 tracks, over 20 VSTi, lots of Melodyne plus heavy plugin chains everywhere, yes I could bounce/freeze but I have no other particular reason to do so. 100% of my CPU load is Sonar, there is nothing else consuming CPU.
 
The odd part is that I haven't seen this behavior in the past, just wondering if it happened after one of the platinum updates.