Ok, been having a chat with tech support - try this - go to Applications > Line6 > Drivers folder and use the uninstaller to remove them. reboot machine. then go to Line6 and get the 7.1.7 driver, not the latest driver and install that instead. I'm testing the driver on mine and so far it *seems* to be behaving.
Whilst I was at it, I reinstalled the UX1 firmware too just to be sure. There's a whole lot more that tech support have sent me, but it is a known fault that they are trying to sort out. Good luck, I will post my findings.
P.s. what interface did you buy? I might get another too!