Thank you SO MUCH. I followed everything on this list and my save has been loading without "content is not present" error anymore, I've been playing for over 2 hours now.
I had not played for several months and had been updating my mods for 2 hours prior to launching my game and getting the issue in question in this topic. I thought I would not be able to play today or anytime soon !
Thanks again for putting this here for us to find