I also had a problem where I was unable to ingest footage from my external drive into FCP.
What I did to get around this problem was to export the files back to the SxS card. Once the files were back on, I used the camera and started to record on the remaining space. I think doing this created a new list for FCP to refer to so the ingestion process would work.
Of course this only works if you didn’t tamper with original BRAV folder.
Hopefully this made sense.