Item Not Saving on Menu

I would try the following:

– deactivate the plugins, and test adding the menu item and saving. If this works, then you can then reactivate the plugins one by one, testing adding a menu item and saving, until the issue happens again. This will pinpoint the plugin causing the issue.

– switch to a default theme, and test adding the menu item.

– resetting the plugins folder by FTP or the cPanel File Manager. Sometimes, an inactive plugin can still cause problems.

I hope this helps!