Server Error in Theme Editor

I just got this message on my forum while editing in the theme editor:

Oops! It looks like something went wrong. Rest assured, our team has been notified of the error.

Go home

It isn't keeping my settings, keeps going to dark theme. I logged out and back in still same error. It doesn't happen while logged out oddly enough. I got it fixed but only by changing something in the editor and saving it. If I don't change something to save the settings, it keeps resulting in that error even after closing out of the editor. It seems to happen in the editor when I switch from editing light theme to dark theme using the toggle in the editor.

I did notice when I change it to dark in the editor my personal setting stay on light, but the forum is dark. Maybe it's a mismatch, my setting is light but it's dark on the editor? I'm no programmer but I think maybe this is the cause?