Bungie Twitter already posted the link but the way to fix the matchmaking it's pretty simple, be patient. Now that sounds like a dumb thing to say but hear me out. As you go into the blind well hallway stop when you get to the large curved steps that go left and right. Go up the right steps crouching and hugging the right wall all the way until you hit the next split hallway. Keep following the right wall all the way until you hit the blind well instance. ( I tested this sprinting, walking, and crouching when you pass beyond the stairs and the slower you went the better the matchmaking worked it seemed.) Tested the theory solo and with teammates worked everytime. It's a weird temporary fix but since it works I won't complain. Edit: You aren't guaranteed to find people this is just the best solution for it. Running in and out will not re-instance your matchmaking but fast travelling back to the main area will.
I just assumed after haf-an-hour standing on top of the central pillar with my moping emote that everyone else had bought the expansion. Still, got some Christmas presents wrapped and did my washing up while my lonely Titan waited in the virtual rain.