I am sure this issue has already been discussed. Some game modes when you download them from Original Author (that have the right settings) get reset after a new match or restarting halo 5. For Example Castle Wars 2.0 Gamemode from OG Author Starts you with infinite sword and 1 plasma gernade. You save that version and play it immediately it works. If you play it again later the settings get erased completely to default. It will still be titled Castle Wars 2.0 but everyone spawns with 2 frags smg and pistol. This happens to a lot of the other game modes as well. Man o War is another I can list off the top of my head.
Didn’t see the official bug thread. I posted this there.