Done some more testing. Removing and reconnecting the USB cable makes no difference, the DAC just isn't detected. I have to power cycle the DAC to get it to detect again, and it doesn't seem to matter if the USB cable it connected or not as once it powers up the machine detects it.
The bug with the wrong sample rate being detected seems to be a permanent fixture now. I can set the windows output to 44.1, 88.2, 176k and it locks in fine, but 48k, 96k, 192k all step down to the rate below and distorts the sound. I used to only get this issue occasionally after a cold start but was never an issue as i leave the DAC running 24/7. No matter what i try i cant get around it anymore which is a real problem.
Using WASPI via foobar works perfectly for every sample rate, it seems like it only the Windows Direct Sound stack that isn't working correctly.