I thought maybe someone would pitch-in with something by now. I don't have any magic setting just wanted to point out that the only time I get blank placeholders is if the site they link to is blocked by my "noscript" addon. For example twitch, tw@tter and pinterest don't automatically open, I have to grant temporary permission for them to show.
The only other thing that occurs is that some people say they need to enable certain cookies on the forum settings - I know nowt about that, maybe that is what you need.