Considering what you have done already, I'd consider getting a RMA from CH.
I agree with Del, it sounds like a hardware issue with the stick itself but before you send it off to CH, test it on another computer if you can. This will help eliminate some potentional causes or help verify the problem.
Granted, it's been many years since I've done CH tech support but the problem pretty much mirrors the symptons of using a USB port that is not outputting the necessary voltage (5 volts), which would cause the exact issue you're facing. Dead pots could also throw your stick out of calibration at random times but usually bad pots are easy to spot during calibration when you move your stick around.
Keep in mind with powered USB hubs, not all of them output the necessary voltage despite being powered. Usually lower end USB hubs are guilty of this, that's why I usually only recommend Belkian USB hubs since I have yet to purchase one that did not output the industry standard voltage.
Another thing you can try to eliminate the USB hub of being the culprit is to disconnect all other USB devices from your system and only connect the stick. Try it with the powered hub and the USB ports on the mainboard, if the problem still exists and you've verified the problem on another machine than you can be pretty certain it's the stick itself. Though usually on the rare side, sometimes you just get a bad stick out of the box.
ack-ack