At least 50% of the time my Windows 10 laptop does not connect to it. Latest drivers & firmware loaded.
 
Task Manager said this:
Windows cannot load the device driver for this hardware because a previous instance of the device driver is still in memory. (Code 38)
The driver could not be loaded because a previous version of the driver is still in memory.
 
Driver Location: Port_#0002.Hub_#0001

This issue requires disabling, rebooting, enabling the drivers in Device Manager or a complete uninstall-reinstall of the drivers to make work.

When you want to disconnect (or power off) the unit, check the "Safely Remove Hardware" icon in the Notification area (lower right).  It may be the device is listed and if you disconnect it without using the Safely Remove Hardware it can cause a Windows status corruption.
 
Another possibility, if you only have USB 3.0 ports there are older USB 2.0 devices that do not work well with USB 3.0 ports.  

Related to fireberd's first suggestion -- check out the utility USB Oblivion.  It deletes all traces of a USB drives from the registry. (Make sure to disconnect any external USB drives first).
 
https://sourceforge.net/projects/usboblivion/
 
+1 on his second suggestion.  USB3 can be a problem with USB2 devices.  If you don't have any USB2 ports, then try all of the USB3 ports.  You may get lucky and find one that's "friendlier" for whatever reason.

Could be any of those. I always turn on the interface before the system and shut the system off before the interface. The interface is USB2. The laptop is all USB3. Windows 10 is supposed to be better at handling USB3 than Windows 7 or 8 and the drivers are supposed to be Windows 10 compatible, but nothing is ever 100%.

I would vote for the PC having USB 3.0 ports.  There are many reports on forums of problems with older USB 2.0 devices and USB 3.0.  Reports here, on the gearslutz forum, I've seen some on the Windows 10 forum, etc.

Would be interesting to know how the drivers work on a Mac, then I'd know to blame Windows or not.

Its not so much the Windows OS as it is the hardware and/or the drivers for the device (which are supplied to Microsoft by the vendor so blame Behringer and not Microsoft).  I have USB 3.0 problems with my MOTU and the problem is not Microsoft its the MOTU drivers or hardware inside the MOTU that is ONLY fully USB 2.0 compatible.  There is a large thread on the gearslutz forum about MOTU specific USB 3.0 issues with their hardware. 

To be honest, I blame EVERYONE.... for ALL my woes.
 
 
 
But that's another story.

So far, as long as I fire up the interface b4 opening Sonar, it works well. No issues for the past 4 weeks.