yes the Windows updates and any anti virussoftware can cause probs, therefore I have an offline dedicated Sonar computer without those and never have such probs....can recommend it.
but you'll fix this prob surely....
have you checked in your Windows hardware configuration/setting that your RME is the only and default audio device ?
Then try ticking 'share drivers with other programs' in Sonar Preferences under 'playback and recording'.
And again, make sure you have only 'analog output 1' checked like I wrote before.
Ofcourse, restart your computer when you change the settings in your hardware setting.
It's some simple setting thing thats the problem, don't worry !