I’m trying to just make a rectangle. It won’t close the right end no matter what I do and I don’t know why.
What have you tried? Have you Joined it before trying to close, etc?
Also, posting the file would enable others to check if there’s something wrong with the geometry.
// Rolf
You probably have overlapping segments joined in there, which means the curve end is not where you think it is. It might even be a closed curve if all the segments are duplicated and joined. What does Properties say about the curve when you select it? You can try exploding it and see what you get as a result - how many segments do you end up with?
If none of that works, post the file.
Could it be GPU tessellations ? DISABLE it?