Not All Pages Showing up in Custom Menus

Are you sure that you published the new page?

Yes, it is published and public. I Googled this problem extensively before posting here. I cannot see any difference between this new page and the rest of the pages.

How many items does your current menu have?

Here are relevant screenshots. Hopefully this will help:

List of all pages: https://imgur.com/X19QN.png
Page that will not show up in menus: https://imgur.com/Hmula.png
Menus page: https://imgur.com/WIiu5.png

Is Blog set to be your main posts page in Settings/Reading?

It is not. But changing that setting still does not affect the custom menus page.

I think you may need to review Creating_a_Static_Front_Page. In the meantime, try changing to the Twenty Ten theme and see if that helps. Also deactivate all plugins. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

Did this solution work in the end, I’m having a similar problem with pages suddenly not showing up in the menu, I’ve tried the methods suggested but to no avail

This was a while ago, but I believe I eventually just added the link in the navigation manually. You can use jQuery to select the menu, then append a new li element to it.