Facebook; This content isn't available right now

I've been seeing this message fairly often on Facebook lately, in certain posts on people's timelines (people who are on my friends' list, when I open their pages):
This content isn't available right now
When this happens, it's usually because the owner only shared it with a small group of people, changed who can see it or it's been deleted.

I never used to see that. I'm not sure what it means. It doesn't seem to show up on posts in my Timeline.

I wonder if it happens when people share other people's content... content whose privacy settings makes it visible to the original poster's friends, but not their friends' friends. But if that's the case, then why does Facebook even display anything to me? Maybe Facebook doesn't let me see the original content, but does want to let me see whatever else my "friends" added (text, emojis, etc.) when sharing it?

I also wonder if it is content that was removed due to being fake or scams, etc.