I've seen in some cases that the list of open documents in a session changes order when reopening the session later. I don't know exactly what causes it, but I think it has to do with closing documents before the session info is updated on disk.

E.g., if I have documents a, b, c and d open, in that order in the tabs bar, sometimes they will reopen as a, c, b, d. I group document tabs by the code functionality inside. It's mildly irritating to have to fix the order the next time.