Bug with "Related Posts" selection

Hi

I think there’s a bug in this theme.

It always shows the same 4 posts for the “Related Posts” section under each article.

You can see it on the demo website:

https://semicolon.kovshenin.com/

and I also have the same problem on my website.

I have many articles, but it always shows the same 4 or 5 articles in the “Related Posts” section.

My question is: is there a simple way to make them truly random?

Thank you.