I've experienced strange issues with the audio loss as well. When I modify ASIO settings within Sonar, or invoke the ASIO panel from other audio programs (e.g. BFD2), I lose audio - no sound, nothing registering on the meters, etc. It's as if the audio engine is frozen - I also seem to lose some audio configuation settings when this occurs - when I look in edit->preferences, some configurations are gone. Only resetting the pc and audio interface restores the sound.
I'm not sure if it's X1a related or not, as I've also just switched to a new audio interface (picked up an RME Fireface UFX) - so haven't isolated whether the issue originates with Sonar or the RME driver. RME believes it's Sonar or BFD2 not releasing the audio driver as required. I figured I'd wait until X1B to see if the situation changes.