I am level 24. Got the Blank Lexicon and Attunement Sphere from Septimus. Both of these items are in my inventory, so clearly I can't drop them.
For whatever reason, the actual pedestal that you're supposed to place the Blank Lexicon in isn't there... I obviously haven't gotten the Elder Scroll yet, because I need to use the Lexicon to do so (but again, I can't because the freaking pedestal isn't physically there...). I have both Elder Knowledge and Discerning the Transmundane in my quests.
Have no idea what the problem is.. On top of that, my last Save (not quick save) is from when I was like level 5, so if I load I have a hell of a lot to make up. I always quick save because I'm an idiot I guess.
I play on PS4 and use mods, but nothing I use should affect the game this tremendously.