Hi Mo!
Man, it worked! Thanks a lot again for the help!
The problem is about the flag $query_string i used after the $request_uri on proxy_pass in the location for the backend. I use this on other applications that I deploy but it seems that for Java/Tomcat works differently.
When I set your configuration, I tried to debug the reason why it works and when I set the $query_string in the proxy_pass, the menu did not display any more. I never thought that this flag could be the source of this problem! I could not believe it when I saw!
The working config is attached.
Do you think we can suggest something to improve the DSpace docs? I believe we can emphasize this in topic 17 of the backend installation and topic 8 of the frontend installation in the apache/nginx configuration section.
Thank you again very much for your time, attention and patience.