A customer reported back the solution to his problem:

USB hub made by Belkin, OS10.3.8
Finally he noticed in System Profiler that after several days the Mbox would jump to a different spot in the USB Tree. Would not show up where it was really plugged into the hub, but was still in System Profiler. It reported at the bottom of the last tree, but not tabbed over like other devices plugged in.

Restart didn’t change the Tree, unplugged, restarted, and plugged back in and it worked.

Of course this was AFTER he’d tried many clean installs of the OS and software.