You might take a look at the pages and how they are configured. Start by looking at the Search page Properties > Navigation > Basic properties. Make sure both checkboxes are checked (show in navigation and sitemap). Next, scroll down to Search & SEO and make sure the "exclude from search" box is not checked.
Lastly, check to see if you have a "robots.txt" file and make sure the URL for that search page is not in there.