The new “Mastery” title that replaces your previous one at 130 only shows up in Forge and Customs lobbies for me.
Same, when I’m in a Matchmaking lobby I have no title.
I’m positive Mastery as a title is only displayed when you’re NOT in a Matchmaking mode like Custom Games, Campaign, and local (and with friends over Xbox Live) Spartan Ops.
Mine does not show either. I thought it was normal since I saw someone else in MM without it too.