This must legitimately be a glitch. I started playing when TDB came out. Just started for the first time and only had a Titan. All of my armor drops for the first few weeks were for Warlocks. Literally every piece. I was the only person I knew of that had his happening. Now I can't believe it was just a coincidence because it the exact same thing is happening to you. A Titan only getting warlock drops. For me, it just stopped happening after a while, so all I can say is stick it out. But there's definitely some bug or something in game, not just RNG doing it's thing like everyone told me.