Error when saving to my library

Exactly what it says. I built a lot and tried to save it to my local Library 

not uploading it online, just saving it for myself, but I keep getting an error. What is happening with this game?

I’m not even running mods. The first time it happened, I hit save again and it worked. This time same process, but it keeps throwing the error. I’m getting really sick of the bugs. It’s exhausting trying to troubleshoot basic features that should just work.

This on top of all the UI exceptions and last exception errors I’m getting in an unmodded game makes absolutely no sense. Not for all the money spent.

Never mind the constant crashing, which I had to figure out a workaround for myself. I'm frustrated and just want to play my game without issues like I was doing just two months ago.

Ps I just picked a tag cuz idk what this fits under