Is there menu items limit? menu location got reset after adding menu items?

You will need to contact your hosting provider about adding these values in “php.ini” file:

max_input_vars = 5000
suhosin.post.max_vars = 5000
suhosin.request.max_vars= 5000

NOTE: Every server is configured to load “php.ini” file from a specific directory, that's why you need to contact your hosting provider about where you should find this file.

Here are some resources that should be useful for you:

1. Can’t add more menu [items] to WordPress custom menus
2. WordPress Trac Ticket detailing the issue
3. The WordPress Menu Item Limit or: Help! Half my menu items just disappeared!