When I load a project everything is fine but after 2 minutes everything freezes, it appears that cpu 10 is 100% at that is what Sonar is using despite the use multi-core box ticked in preferences.
As soon as Sonar is killed cpu 10 goes back to zero. its a 6 core PC with 12 threads, 64GB RAM, i7 processor running Windows 10.
Anybody got any ideas?

What sound card and driver mode are you using (asio or wasapi)? There are some issues with dynamic arming that on some systems can cause the performance metres to peg and playback to fail under wasapi exclusive mode. 

There should be no issues as my backup PC has exactly the same hardware config just less memory and a less powerful i7 processor and Sonar works fine.
But I placed a support call with Dell they updated the BIOS and it's now running sweet as a nut across the cores. Bit suspicious as it's the 1st thing they tried so might have been a known issue......
Of course now the creative spark has passed...................................

Okay it's definitely using multi-cores now but once I open up the plug-ins themselves and attempt to make a change the screen freezes once again although Sonar quite happily continues to play the music. This is at the moment a simple project with only 2 tracks but cpu is 26% for Sonar which seems a bit excessive to say the least. My best guess at the moment is that the plug-in is being loaded in a cpu that's already heavily utilised instead of one that's doing nothing in fact the same one SPAT is in.

I have loaded a more complex project and it almost immediately freezes, but if I select close window for Sonar from windows it appears to momentarily in-freeze, BUT nothing is now playing at all and yet SPLAT is showing a cpu usage of 20% what is it doing?
This looks wrong and maybe the reason I am having issues something is running in the background on SPLAT anybody got any ideas?

Just to confirm SPLAT is showing audio processing of 20%+ and there is no processing supposed to be going on as nothing is playing at all.

Have analysed the threads and there are a whole load of these running.
ucrtbasedll!o realloc base+&K20 all at around 0.7% which when totalled up takes up 17% of cpu? The rest a pretty small and are plugins at around 0.01% or so the rest are the remaining plugins at <0.01%.
 
So the question what are these ucrtbasedll!o realloc base+&K20?
 

Have run same project on back-up PC and seeing usage of 13% CPU BUT it appears to be balancing across cores correctly so no freezing occurring.  This still begs the question why on a more powerful PC it is running at a higher CPU rate. Interesting if you uncheck "Plug-in load balancing" the cpu load drops significantly.
 

Hello,
In your audio.ini file :
  
ThreadSchedulingModel=<0 - 2> 
Type Integer 
Default 1  
 
Change this setting to 2 if it is not.
 
Also is this windows 7 or 10.. If 10 see this link. :
https://support.focusrite.com/hc/en-gb/articles/207355205-Optimising-your-PC-for-Audio-on-Windows-10
 
It was very helpful for my new build  Thanks
 

Thanks for the advice will give it a try, in any case I have also now allowed SPLAT to use the overclock option for the cores so that should give me some headroom.