Thanks Craig,
I confess I had to look up what a "Toast Notification" is and I'm still not sure if I would need to be connected to the internet to follow the process through (obviously I have the internet connection disabled when working in Sonar).  But if it comes up again I will follow your advice.
 
@gswitz
Thanks buddy, yes it is a laptop and I checked Device Manager > Network Adapters > Properties but there were no Power Management options.  Is it similar to the Minimum/Maximum Processor State that you find within Power Options?  I have both of those set to 100% when plugged into Mains.
 
The changes appear to be working so far (highest Interrupt To Process Latency is currently 236µs after nearly 2 hours - much improved compared to the 1100µs I had earlier), but I plan to leave Latency Monitoring running all night and then we'll see in the morning.
 
Thanks again for all the advice.

https://youtu.be/eOVuzOja-yE
 
I made a video in case it helps.
 

On most laptops I've disabled just the Wi Fi, using the toggle and I always disable Battery management in device manager. 
HDMI audio is now also on my list and I think that's on your report is it not? 
There is a audio drive used when you hook up a monitor or projector using HDMI and that driver is pesky. 
 
But I would also question the stability of the Roland driver. That's sucks that they tell you to let windows update deal with it. I don't buy that at all. 
 
You might want to try running in WASAPI eclusive mode as it will certainly work for just recording. 
I record 16 tracks of audio to a W7 laptop in WDM mode all night long without issues. That's using a Tascam interface. 
 
I would also use a wave editor for plain stereo recordings, much lighter load and simple to use. 
Wave Lab will auto number the tracks everytime you hit the spacebar so you can break it down into shorter tracks but never miss a second of recording. 
Either that or pick up a Tascam or Zoom handy recorder, they are bullet proof. 
 

Under Windows 10, lots of devices are class-compliant, and Microsoft does just handle it for those, pretty well.
 
There DOES seem to be some wisdom in trying performance out with HD Audio disabled, as well as the WiFi, and for some the battery management too.
 
2 other suggestions - 1) try temporarily disabling Avast right before launching a Sonar session, and if performance improves - consider adding paths to the folders Sonar will use (sample libraries, projects folder, etc) to Avast's Exclusions list of folders to not scan, and that might help a bunch too.  Avast will still evaluate every file you open or create otherwise, which can really hamper Sonar performance.  2) I would suggest dropping your ASIO Buffer Size from 320 samples down to 128, and see if that helps.
 
And, you are not using any Pro Channel modules when recording?
 
Bob Bone
 

SG : there is a letter missing in your model number you posted (Asus X556U<<< ? .. how have you made out so far ?
https://www.asus.com/Note...6UA/HelpDesk_Download/

Make sure you are connected to a USB2 (not a USB3/blue) port.   

The Realtek PCIe GBE Family Controller IS the Ethernet port/network controller I disable... if that helps. That, combined with disabling the onboard sound and sound on the video card/hdmi (High Definition Audio Device) is what made my laptop great with Sonar.

Guys,
The good news is that running Latency Monitor overnight, it still says it's OK for real-time audio.  The highest Interrupt To Process Latency was 380µs and from previous runs, it seems that 1000µs is around the threshold where it says "your laptop seems to have a problem with real time audio".  So things seem much improved.  I think the next step will be to do a long audio recording test (record the TV maybe) and check that it remains stable.  Will report back soon, I have a lot to do today so please forgive me if I don't get back until tomorrow (earliest).
Thanks for your all your feedback guys.  
Geoff, that was amazingly generous of you to post an excellent video on Youtube (I was not expecting that!), I really appreciate you taking the time.
 
p.s. Feedback on other posts:- good tip about using the USB2 port rather than USB3.  I've changed my signature to reflect the full id of my laptop.  I will have a think about Avast and disabling searches in certain directories.  I am not using Prochannel when recording.  I will also think about whether to drop the sample size if it becomes necessary.  Thanks to all!

ryecatchermark
...combined with disabling the onboard sound and sound on the video card/hdmi (High Definition Audio Device) is what made my laptop great with Sonar.

The latter can make a huge difference with laptop and desktop systems...or no difference at all, depending how aggressive the driver is about controlling your audio. In my case, disabling the "HD Driver" was extremely beneficial - it allowed for much lower latency. 

Anderton
Wait until there's a dropout and you see a Toast notification. Click on the notification's Help button, and it will give you a list of things to try. When I reached the section on recommendations for disk cache tweaks, and then made changes as instructed, my dropout problems stopped once and for all.

this sounds really useful - are the tips system/dropout-specific, or just a set of standard tips that are always shown?