I tried using Relevanssi plugin on my local WordPress test installation.
After the plugin was installed, the search didn’t return any page results (i search for a particular page name).
Then I went to “Settings -> Relevanssi” and under “Indexing options” checked if the “page” has tick on “Indexing” column. It did have, so I clicked on “Save indexing options, erase index and rebuild the index” button.
After that, the search found a page with the name i searched for.
Try the same procedure on your website and everything should work.