In your particular case… I’m not sure if you also needed to save the assets. (Since you didn’t mention that.)
This would at least have prevented the crash, I think.
Though, I made this FREE plugin tool that fixes the “Unknown Structure” problem.
I don’t know if it would have helped you in your case… but it’s worth trying perhaps?
Check this post for all the info you’ll need: “Unknown Structure” FIXER! - FREE Plugin Tool"
Good luck everyone.