I am running a 2012 12 CORE Mac Pro running Sierra with 64gb of memory. I have updated to 2018 Premier Pro CC and 2018 Prelude CC. I can ingest Canon MXF files, but after while when I scrub through clips in Prelude and after export to Premiere Pro via Prelude, I get portions of the clip in Red and also clips that can't find the media. The media is sitting on internal Toshiba 4 TB drive (Brand new/sleep mode turned off). I had same problem on an HGST 6 TB drive (New in December 2017)in the same machine.