ucrtbase.dll is part of the C runtime library, which in turn is part of Windows. I wouldn't be surprised if the problem ultimately turns out to be a plugin that doesn't play well with load balancing.

You should not worry about overclock option or processor. This is not likely the processor issue. I will bet on bad or corrupted plugin. Load Sonar in Safe mode. Don't remember how, but it will load Sonar without plugins. Then go ahead and unable one plugin at a time. When it crashes, you will know what caused it. Also look in plugin manager what plugins it finds after the scan. Also if your processor overtclocked, make it back to stock settings.

Thanks plug-ins may be the underlying issue as I loaded just my template and that was running at 19% CPU. As this is the replacement PC for the one that went into meltdown there might be some plug-ins that have yet to be activated  so have started walking through each one and checking. At least while working on template I have room to manoeuvre there were some that caused issues previously but those were not installed initially.
I would suspect the PC but it runs high performance games without raising a sweat.
 
For info.
Windows 10 64 bit (one build behind latest), i7-68000K 3.4GHZ CPU(4.0GHz overclocked) 6 core 12 logical processors
64GB RAM, Dual GTX-1080 graphics, ZxR DB Pro soundcard. 1.4TB of SSD and 6TB of SATA.
 
The backup PC is a Windows 10 64 bit latest build a less powerful i7 3.4GHz 6 cores core 12 logical processors, 32GB RAM single less powerful GTX graphics card and same soundcard, and 1,256GB of SSD and 4TB of SATA.
More plugin-ins on backup (the troublesome ones) and all external hardware midi keyboards, console 1 and mixers etc.can be connected to either.

At last getting an insight into part of the problem. Sonar always loaded in cpu 10 for some reason and then I spotted when excel was in cpu 10 it also was slower. So removed the affinity for Sonar to use cpu 10 & 11 and hey Presto running at over 20% but balanced across other cpus. So we have a hardware fault on core 5 which also explains why I`m seeing higher cpu on this pc as not all cores are running. Now to invoke warranty and get my liquid cooled processor replaced.

Done further testing and SPLAT is happily playing my midi instrument sounds are coming out etc. , but the screen is frozen. There is plenty of CPU even in the processor SPLAT is running in so it starting to look like an incompatibility with the NVidia Dual GTX-1080 graphics card, at least there is no other common denominator between the 2 replacement PC's. Anyone using same graphics cards? 

Some plugins use your GPU, not for its intended function but as a parallel CPU. It's great when it works, but some video adapters (GeForce in particular) can have problems with it. Waves, FabFilter and Meldaproduction all do it, and all of them have had issues in the past with specific video cards. I don't know of any soft synths that do, but I'm just not that big a synth guy.

Trouble is this is happening on a basic template with one instrument. But there are reported issues to do with stuttering occurring on the video card so will raise a support ticket with NVidia.

Now I've entered the Twilight Zone. There was a new driver update for Nvidia which I installed and for some reason caused a system restart.
I then did exactly what I did yesterday with SPLAT and 2 things happened.
1. No freezing at all (okay maybe Nvidia have fixed the stutter bug)
2. SPLAT from consistently using 4%CPU yesterday has now dropped so low it's not measurable (Twilight Zone)
Even loaded 2 instruments and pinned both and everything is still stable.
Just need a reality check now so making sure Hilary Clinton is still president and we voted to remain in EU...........

If you're basing your CPU percentage on SONAR's CPU meter, that's misleading. It doesn't really display how much CPU SONAR is using, but rather how long it takes SONAR to fill the audio buffers. It's still a useful indicator of how close you are to maxing out your CPU, but it's a number that can be affected by other things that are going on in the system.
 
So no, you're not in the Twilight Zone. The White House Science Committee is still a roomful of empty chairs.

No I`m using lasso pro to monitor the entire system, what is interesting is that if I load another program and leave it open on the monitor SPLAT usage goes up to 1 - 2% which seems to imply the GPU is passing back some of it`s processing to the main CPU. Definitely looking like a driver issue on the GTX 1080 with SLI enabled and there are still a few bugs according to internet. Anyway at least SPLAT is now working properly so time to get the mixes done.