First, try refreshing your feed. Just pull down on the screen to refresh. If that doesn't work, clear the cache of the Facebook app. The steps for this vary depending on your device. For example, on an Android device, you can go to Settings, then Apps, find Facebook, and clear the cache.
Well, it could be due to an outdated version of the Facebook app. Sometimes new features, including the proper display of stories, require the latest version. So, go to your app store and check for updates. Also, if you've recently changed your account settings in terms of notifications or story preferences, it might have affected your ability to see stories. Make sure all the relevant settings are set to the defaults if you're not sure what went wrong.
Yes, it is. On the Facebook mobile app, you can use the same methods as on the desktop to some extent. Check your profile, look for the Memories tab if available, and use the search function. The app layout might be a bit different, but the general principles apply.
Yes, usually. If the privacy settings of the story allow it, comments are visible. But sometimes, if the person who posted the story has some special settings, like hiding comments from certain people or disabling comments altogether, then you might not be able to see them. For example, if they've set their story to be visible only to a specific group of friends and disabled comments for others outside that group.
There could be a few reasons. Maybe you unfollowed or blocked some sources of stories by accident. Or, FB's algorithm might not be showing you the ones it thinks you're not interested in. You can try adjusting your interests in the settings.
It's possible that the algorithm that decides what shows up in your news feed has changed. Maybe you haven't been interacting with the types of posts that usually show up as top stories recently. Or, it could be that your friends and pages you follow haven't been posting much of that kind of content.