I got disconnected from the servers while running a strike and had to completely restart the game for the servers to allow me back in. Right after signing back in I was prompted to rejoin my previous activity, so I selected yes. Then I was thrown into the intro for the Lightfall campaign. I don't know if this was a UI bug or the games weird mechanic of auto-starting the current campaign after one or two sign-ins if you haven't already started it. This issue has been around for a while because I encountered this same problem with Witch Queen.