Custom game modes don't work

I’ve followed the 343 favourites to get the maps and game modes but whenever I put the game modes on that I’ve bookmarked it will not let me start the game, or save a copy of the game mode, any reason for this??

im having the same issue and still cant seem to find a resolution for this

There’s a bug. You have two options. Load the base game mode that they used to build it first (such as Slayer, or Strongholds), then load the custom game mode from your bookmarks. If you guess the right mode, then it will load up. Alternatively, you can load the file directly from the Author’s Files instead of your bookmarks.

343 hasn’t even acknowledged this issue, which is incredibly frustrating.