Error : Quick launch -- change order

I have a user getting an error when using the "change order" button on the "quick launch" menu (see attached.

 

This is for sharepoint online.

User is site owner with full control.

 

My account (with site collection admin rights) can use the button.

 

I found a similar issue

https://sharepoint.stackexchange.com/questions/29499/access-denied-error-change-item-order-links-list which seems to suggest I can change the permissions on the list directly, but I cant see how/where to do this.