AllanH
I chose to not install the "feature update" that I believe was being delivered, in stead just taking the security release. Sonar is fine for me.

which feature update? there wasn't one unless you were not current.
 
March 14, 2017—KB4013429 (OS Build 14393.953)

Improvements and fixes

This update includes quality improvements. No new operating system features are being introduced in this update. Key changes include (more here)

Apparently there is a bug in Tuesday's update that breaks numerous audio and video applications (specifically DirectShow, for which a non-specific "security update" has been applied).
 
Fortunately, the applications affected include Windows Media Player. That's fortunate because while MS might not place a high priority on a bug that just affects DAW users, WMP is a whole 'nother matter.
 
FWIW, neither SONAR nor WMP have been impacted here.
 

My puter updated Tues and again today. I just got a crash with the error in the "CompPkgSup.DLL" module, while trying to import an MP4 file.

Yup, that's the one, SF. Sit tight for a few days, I'll bet that problem magically disappears next Tuesday. It seems to be getting some attention over at MS, as it apparently can cause Explorer to crash, too. That's the kind of bad news that mobilizes emergency patch teams. Follow that first link and go to the second page, where someone has posted a possible workaround.

Did a quick search, it looks like this CompPkgSup.DLL (WMP) issue was spotted early February, so it looks like a known bug that has resurfaced in the latest update. Good new is, like bitflipper mentionned, it got fixed quickly the first time around.
 
 

All Win 10 updates installed here, no OS-related issues to report.

All fine here. Apart from one old PC on win10 home repeatedly failing to install ... my main DAW works just as before (and definitely better than during the november win10 update mess)

All fine here. Apart from one old PC on win10 home repeatedly failing to install ... my main DAW works just as before (and definitely better than during the november win10 update mess)

I did the win10 update and updated sonar and every time I try to drag track templates from the sonar browser I'm crashing out. 

I had a different win10 debacle last week. I only connect to the internet for sw updates. Just got a focusrite 6i6, came with a bunch of plugins. Plugged in the usb adapter and, no internet access. Did the research, pages and pages about this… 
On the phone with ms for hours trying every net-related fix, nada. So yesterday I decided to try a different usb port again,  had tried that on Thursday, didn't work, but somehow it did. 
With ms you never know… 
On a new ssd drive with a fresh copy of win10, 4 months old…