Same here - Fact or Fiction is still unfinished in my journal. 'Search kett database' is checked off, but 'Disable security matrix' is the next step and I can't complete it. After working on the 'Remove the Heart' mission, I had Fact or Fiction markers active, but the markers went away after I completed it, even though I went to the top room and activated the console after finishing the "boss" and unlocking the elevator etc. I have been back and spoke to the historian, and said something about the data being destroyed, but saw that Fact or Fiction was still unfinished. Went back to the kett base twice now to try and see if it would somehow re-activate, but nope. I'm going to say this is definitely bugged, unless there is some sort of very specific sequence that needs to be followed to be able to succeed <- but if that were the case, it should have been marked as failed in my journal at this point, and not active.
Edit - Platform is Xbox One