I did not have this happen to me…but when I had an issue with a menu here is how I got round it.
I went to the page in question and copied all the html so I had a full backup of the page…I then deleted the page and trashed the menu and started again.
I remade the page…easy because I have the html code…I called the page something close to the original, I then created a new menu and called that something different from the old menu name, linked it to the new page and problem was solved.
Now although our problems were/are not the same, do you thing this may fix yours?