Once you hit Champion in Slayer it's very common to not find games until 5 minutes of searching. They need to delete redundant playlist like social slayer and stop punishing players who play the game a lot but making them unable to find games once their MMR goes into the top 200 players. All my friends who are Champs in Slayer have this same problem and many times we are unable to play together because of this. Thank you, I love Halo 5 and want to be able to play!
Can't Find Games In Slayer