Ok... this is way way worse than I thought...
The mission is with Laura Lockhart, and as soon as you take it, she is gone, and you can't call her or find her. She is inside the mission at this point. When you go inside, it starts off like normal but you run into a door that can't be opened without a key, and it never drops. SHe is on the other side of that door somewhere. When you leave the mission, you discover that the Abandon button is grayed out. You can't abandon the mission, nor can you call her to complete it (the once every 3 days auto-complete option), and you can't finish it. It is seemingly impossible to get rid of this mission. I may forever have this mission stuck in my queue taking up space from my available missions! With no way to report a bug, I'm not sure what to do but post here. The missions is "Defend the UNSF Base", the contact is Laura Lockhart. It is in Steel Canyon.