Pages missing from dropdown list

When I go to the plugin’s settings, I leave the theme the same and I just want to change the page. When I pull up the dropdown of all the pages, only some of them are there. I must be doing something that causes about half of the pages not to be listed. I’ve tried even using existing pages and just clear it and the original page but then it will disappear. Also – how do you change the theme to one page and it not effect the entire site’s pages? Thx!

The page I need help with: [log in to see the link]