Today I was gonna play some Slayer and rank up a little but the I saw that once I had clicked on ranked only the HCS playlist was available! I want answers 343! And also please put this information on message of the day!
Did you try a hard reset if the Xbox?
There is a glitch that causes some lists not to load, it is rare, thankfully, but a hard reset of the xbox, or quit and restart the game will fix.