Space looses menu

Good Morning,

I have a user that has created a space and content etc. Today when visiting the space, the menu has disappeared. I can see tge space, the content is still there. I can see the content via the config panel, but the menu is now empty. I can see the menu tree if I look at a piece of content. How can I restore the menu to the space pages.

What might have happened to cause the menu to delink/disappear?