Thanks for answer.
try using the "rebuild" button in your menu manager
: I have already try, without any change or success...
Actually, I can't say that FlexiCOntent have deleted my menu, it seems rather that it goes back to its initial statement.
I explain: to create my main menu, I have used the default "FlexiContent Hidden Menu" that is created when FlexiContent is installed in Joomla. I have unpublished the default "Content" menu item and add all my alias menu items. And everything was working fine... once I added the Advanced Search menu item and was setting it.
The result: the main Menu itself wasn't really deleted (it still have the same menu type name), but goes back like it was before I begun to change it, with the default "Content" menu item reactivated itself, and all my menu items (alias and others) deleted...
Note: between the time I've created the menu items and when they disappeared, I didn't deleted any contents, modules or plugins.
I did drag and drop some menu items, but the menu was working fine after.
The issue appeared only when I tried to save my new setting of the Advanced Search menu item... :huh: