The footage plays fine on camera. It is 60fps HEVC 10 bit 4:2:2 from a canon r5
When I reimported with Eos Utility 3 it plays back fine. So, I would assume it was image capture and chock it up to that and move on, however I uploaded the files from both importers and they all played fine on a pc(AMD Ryzen 7 3700x, Nvidia RTX 2070 Super, 64GB RAM, various NTSF drives - this was running off an external HDD (5400rpm)). When I shot two test files one 4k-U and one 4k-D both played back fine. So, it's not the codec alone.