Maybe I have a solution. This happened to me several times after updates. First time it takes weeks and I lost all my stuff. But then @sestus2009 told me to re-download the siptah dlc. Thx for that!
Go to the psn store or the game library and there is a button ‘add-ons’ or something like that.
There you have all your conan dlc listed with a download arrow right of it. Even if siptah download arrow is greyed out just push it and download the siptah dlc again. After that you should be able to load into siptah again.