Hello there! I've been working on a website lately and noticed that when I want to create a menu, it won't show up in Menu List under Pages/Menus. Although at the Overview tab I can see the menu's title. Reopening the menu to edit, there's no menu name. Because of that, I can't add the menu in Menu manager. I've tried to modify a default menu, created at install and it disappeared from the Menu List, but because it previously had a menu name, I was still able to add it at the Menu Manager.
Another problem is that if the menu is set to Default style, only the title is shown, the content is not.
Background info: I use only default plugins, but a custom theme is installed. Also, I translated most of the language files to my mother language, but no error message is shown.
EDIT: I've looked at the database tables and the menu_name is empty. However if I set it manually in phpMyAdmin, it shows up as a menu.