It appears transcoding the footage to DNX-HD and re-linking it as the master file has done the trick.
Unfortunately, it appears my Power supply or Motherboard has gone kaput, so I am off to solve new problems.
I’m having the same problem. I’m working on a film that has a few scenes that were started in Premiere and I want to move them into Final Cut so I can insert them into the master movie in Full Res.
I selected square pixels as the Aspect in the Export window but the Output still displays the black bars