If your Facebook Page is using an old URL format (see example below), it may fail to load in web views within your app. To update your page's URL, check out Facebook's help desk article.
Old URL Example: facebook.com/chipotle-687129241432291/timeline/
New URL Example: facebook.com/chipotle
Once you update your Facebook Page's URL, be sure to change every instance of it within your app. After you've made your changes, refresh the app on your device and test once more. The page should begin loading properly at this point.