If you're listening to sources other than SONAR, the sample rate may be different. I don't know how the Focusrite handles sample rate changes, but that could be an issue. 
 
Check the Windows Sound control panel for your playback device's properties (bit depth and sample rate). Try setting it to the same as what you use for SONAR, or vice-versa.

Isn't this whole thread from Oct 2016 about dropouts with the Scarlett?
http://forum.cakewalk.com/Focusrite-Scarlett-2i4-USB-audio-interface-Dropouts-ASIO-and-other-questions-m3498363.aspx
 
I'd say those problems are still problems.

msorrels
Isn't this whole thread from Oct 2016 about dropouts with the Scarlett?
http://forum.cakewalk.com/Focusrite-Scarlett-2i4-USB-audio-interface-Dropouts-ASIO-and-other-questions-m3498363.aspx
 
I'd say those problems are still problems.

 Yes, one thing stood out to me that thread,
 

Tripecac
 
I actually have 3 audio cards connected to the PC at the moment:
 
1) ASUS Xonar DX (PCI card)
2) M-Audio Delta-44 (PCI card)
3) Focusrite Scarlett 2i4 (USB)

 
This is bound to cause issues.
 
I believe Focusrite had an update last month (in June) for drivers though. it might be worth checking out.
there is a second Gen firmware update as well if I recall correctly
 

Some updates on their Beta website as well
http://beta.focusrite.com
 

I had similar problems as the OP with my 6i6 Gen2.  New beta drivers from tech support solved it, (so far...).
 
HTH
 
Paul

Craig may be onto something with sample rates changing. The first thing Focusrite tech support will ask you is which sample rate are you using and then they'll caution you about using their device to run Windows sounds in the background. I have an M Audio 2496 on my system that handles everything but SONAR to prevent conflicts. 
 
One thing I did find out with the Scarlett was if I powered it on after Windows booted up it would redo my sound configuration, meaning it would take over everything on my PC whether I had it assigned to the M Audio or not in control panel.
 
As a side note on my desktop I have a PCIe to USB 3.0 card that I use for audio so my USB devices aren't sharing any bandwith.
 
 
 

I just tried Sonar, and after about 10 minutes the problem happened again.  I restarted Sonar, and again it happened after a few minutes.
 
To clarify, when I say "dropout" in this topic I mean the sound completely stops, and doesn't come back until I restart Sonar.  It's not like a momentary dropout, a short interruption in the sound (usually resulting in a pop or click).  This is a complete cessation of audio, probably from either the Sonar audio engine or the ASIO driver.
 
My sample rate in Sonar is 44 kHz.  The Audio Driver Bit Depth is greyed out, but says "24".  I cannot change that value.  Samples are 256, with an effective latency of 5.8 ms.
 
I forgot about the M-Audio and Xonar cards.  I have now disabled them using the Device Manager.  However, within about 2 minutes, the problem came again.
 
I notice that the CPU activity is high.
 
Also, changing the ASIO from 256 to 128 samples (and back) does not fix the problem.  But maybe that doesn't really reset the ASIO driver.
 
I'll give the beta drivers a shot.

Actually the beta drivers seem to be older than the current driver version (4.36.4), which is what I have installed.
 
Or are you referring to the beta firmware (version 1.0b1 on 27 April 2017)?
 
Paul, what driver versions and firmware are you using now?
 
 

Do you get this issue in all projects or just one? The CPU load increase at the same time suggests that maybe it could be a buffer issue. Maybe you have some plugins running that are very resource intensive? What happens if you increase the asio buffer to max - e.g. 2048?

I've been using Drumlab for the first time (since it was in Komplete 11, which I got recently).  It sounds great, but I notice it uses about 30-35 voices, which seems a bit high for a Komplete Instrument.
 
If I increase the ASIO buffer from 256 to 2048 the latency would go from 5.8ms to 46.4ms, which is pretty horrible for tracking (but okay for mixing).  Are you suggesting doing it as a test only, not a permanent change?