Hi Mt Spokane.
Op says it is a 5DIII which will take a Compact Flash and SD card, no Cfast card so no fix? Also it happened on both cards which would take a real huge dose of coincidence for both cards to fail together, to me this would suggest either a power interruption, loose battery grip or something during a burst write process or a more serious issue with the camera, but I'm really only guessing based on the information given.
Cheers, Graham.
Mt Spokane Photography said:
Is it on your backup card as well? It looks like a typical card error, it could be a download issue, or a card issue. Have you updated the Camera Firmware for the Cfast card issue? If not, update it.