T4R. I works with the standard 343 gamertypes and a couple of files I have saved myself, but none of my bookmarked gametypes work. The maps do, but the gametypes don't. Even if they are meant for that map. I select them and they don't load or show up at all. What do?

You have to select the 343 base gametype equivalent first.  So if are playing a slayer variant, select 343s slayer then load your game type.  It's a bug they still apparently haven't fixed.