Untraceable build, won't load?

I was playing an H4 mission Forerunner, completed it and the next level Infinity, loaded but after the opening cutscene the screen went black with tiny red words at the top left reading “untraceable build, won’t load”. Then the game restarted and loaded the main menu. Has anyone encountered this? What does untraceable build even mean?
Edit: happened again going form Reclaimer to Shutdown. It’s an easy reboot, I’m just curious as to why/what it is.