get_next_posts_link() returns no result despite available posts

I am developing a custom theme based on the Genesis framework. I want to display a ‘previous post | next post’ navigation below any article in the single post view. However, neither get_next_posts_link() nor get_previous_posts_link() return any value. All output I can see is

|

Of course, there are adjacent posts available.

My code looks something like this

single.php

Can anyone point me in the right direction?