Adam, im not sure if I mentioned but don't rule out a bad USB port or bad USB able.
I wore a port out a while back and it difficult for me to find out what was wrong because the port was the last thing I expected but when we plug in our controllers, interfaces, exc in to a port a million times they get wasted eventually.
Of course this doesn't explain why it works with VSTs but not sonar. (maybe sonar is just finicky)
Also not sure if mentioned but don't use a USB hub.
Also important to sonar but not as much vst's, make sure to always plug the controller in to the same port you used to install the drivers. you will get it to work but inconsistently. Some devices are plug and play so that doesn't always apply.
I haven't experienced losing devices but I have had sonar hold my controller hostage a while back with an M audio Oxygen 49. However once I built a new system the problem disappeared. I blamed the combo of Sonar and the set up (An AMD FX/Gigabyte Mobo).