Not sure what triggers it, but for some match recordings, your armor (though in my case it varied per life) gamer-tag and service tag get replaced with some random person’s, and you (both your GT/ST, and thee one replacing it) don’t show up in the scoreboard.
Someone else has a video showing off the issue: Halo 5 - Major Theater Problem - YouTube
It’s worth noting that in my case, my armor did stay the same for most of the game, only my GT and ST were different, but occasionally I would spawn with a diffrent helmet throughout thee game.