I have the same issue.
Firestudio Mobile => FW400 => adapter => Thunderbolt on a MacBook Pro running 10..14.1
Worked flawlessly 2 days ago in a studio, came home, Na not gonna work.
Tested it on my iMac under 10.11 and FW400 - perfect. I don't think my adapter is faulty as the unit lights up but the synching is not happening.
I've submitted a request to the Tech people but nothing back as yet. Sick of un-installing, fiddling with the Library, re-installing, rebooting, trying earlier version of UC - all to no avail. C'mon guys, I've got work waiting!