than it must be additional plugin , any extensions using plugins ?
I don't understand the question.
If you want to know if I am using extra plugins, then "Yes" I have many of them that I added.
Also, I have other components and modules. That Mega Menu is an Extra Plugin anyways.
If the question is whether the menu is linking to a plugin or extra new component. The answer is "No". I am only linking to a simple article or category. I am not even adding any fancy stuff to the Mega Menu, just using it to link to the core Joomla Sections and categories.
I thought that it was something to do with the Arabic language, but I tested with English and I had the same problem. I added menu item test 1 to the main menu, it worked.
Added the second menu item linking to a category, test 2 it worked,
Added a third menu item test 3 linking to test3 category, it worked and when I add the fourth one, the site goes blank.
I made many combinations. Linking to categories, sections, external links, nothing would work.. that fourth menu item is not wanted.
I am reinstalling a whole new fresh Joomla in a different folder and putting a new template etc... I am not sure whether I will manually recreate all the categories, articles and menues or just copy the database... I will let you know what happens.