pixelated video clips while editing with final cut

Seeing an issue where some clips are pixelated during the Final Cut edit mode. Sometimes it is the entire clip, more often it is sections of the clip. All of the video media is from a Sony FX-7 camera, recorded in 4K, 23.98p fps, using Cine EI with SLOG-3. This appears to be happening ONLY on one Mac: a 2020 Mac Pro tower. I have physically moved the RAID containing the Library to a 2024 Mac Studio and tested. It also shows the same issue with the same clips. We have 4 Mac Studios and two Mac Pro towers in our shop, all using Sequoia and Final Cut ver 11.1, with media recorded on the same camera. We are only seeing this initially with one Mac Pro as all the others have worked fine with the same type of camera source media. While the source media is 4K, we edit to a 1080p, 23.98p frame rate timeline.

Now, if I right-click on a clip I see pixelated in Final Cut, and choose Reveal in Finder to bring up the clip, I can playback that clip in QT and it's fine. No pixelation. I have tried optimizing the clip and it usually makes the pixelation worse (e.g., instead of a section of the clip, typically corrupts the entire browser clip.) There are some instances where the browser clip plays back fine in the browser but when inserted into a timeline, pixelation will occur.

I have tried dumping the suspect clips and re-importing. This is hit-or-miss but more often than not, the same pixelation occurs but in other areas of the re-imported clip. I am also wondering if the issue lies with the OWC ThunderBay IV RAID, which utilizes Thunderbolt 2 port connection. In this setup, we use a Thunderbolt 2 cable from the RAID that connects to the Mac Pro via an Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter. Wondering if there could be speed issues?

Has anyone else experienced something like this? Note, I am not talking about seeing pixelation when exporting videos but actually when trying to edit in Final Cut. Thanks so much!