Thank you so much for contacting me. I really appreciate the help with this matter. After repeatedly scouring the forums and internet for any info, I felt my only recourse was to begin from scratch and create a new menu and replace, one by one, each page (sub menu items). Even though I was able to reposition many of the pages, it appears that it will not support any more than 85 in total. But the day before this all happened -- an no to both answers 1. no one else has access to the blog and 2. I have not switched themes ever -- I had a total of 159 sub menu pages. I have cleared the cache a half dozen times to no effect and logged in from other computers using different browsers (I find Google Chrome to be most effective for me).
Now, every time I add a new page under any of the sub menus, whatever is at the bottom disappears. One replaces the other.
Any other thoughts?
Again, many thanks for your support.