2013 – Unable to add/remove items in Global and current navigation in SharePoint online

I am trying to add items in Global Navigation in a SharePoint online site.

When I goto site settings and Navigation under look and feel (/_layouts/15/AreaNavigationsettings.aspx), I see empty Global Navigation and Current Navigation.

When I add something (Link & Headings) under it and click ok, it is not getting saved. Even when I click on edit links on left navigation and add a link and save it, it is not getting saved.

Not sure what the issue is, any guidance is appreciated. TIA