Hello at All
If you need the Loopback function, you can stop reading now.
My Setup. iMac2008, El Capitan, UR22 MKII, using Cubase AI8, Garagband10 and Reaper.
I´ve tried everything do get rid of my nasty Clickings caused by Dropouts.
Tried different/ older drivers from Yamaha/ Steinberg without success. Than i uninstalled the Steinberg/Yamaha USB driver and:
Tadaaa… the Dropouts are no more on my system
The Interface is now running by the mac core driver. Even with a little less of latency, but you might finetune your latency correction manually a bit in the preferences of your DAW. For me, +2ms and 109 sample are spot on now.
And check youre system settings after uninstalling the other USB driver, because my first recording was first automaticly set to 24bit 192khz by default! So if you´re using the system settings with your recording settings, be aware! 
If you need/ want to now more about it, i wrote a longer, more detailed “story” here: UR interfaces audio drop outs (follow-up thread) - #96 by DonGrappo - UR Series - Steinberg Forums
After searching so long for a solution to my problem, and got a fast response from steinberg, but with no solution for me, i thought i put my experiance in a new thread and i hope my solution will be helpfull to other people with an dropout issue.
Greetings from good cold germany 
Wänä
P.S. ::but this solution might not work for you, because it can be caused by many other things too.