I had this problem. I actually disabled the lock screen, and it went away months ago. Today it came back. I hate it because it not only brought back the lock screen, but because I have to swipe right twice to unlock the phone, for some reason. The app causing it was called "Headlines". I uninstalled the updates for it, but the app remains. I clicked the options for it, and one of them did the trick. I am not going back to find out which one, no way.