On my local with the latest Discourse version, it works as expected.
Indeed, nothing happens on your forum. Looking at the HTML, it misses the user card link, e.g.:
<a data-user-card="Arkshine"> <img.../> </a>
From what I see, you’re using Discourse v3.3.3.
The latest version from the stable branch is 3.4.2.
I would try to upgrade first.
Edit:
I can see it has been fixed here in v3.4.0+ by Robert:
https://github.com/discourse/discourse/commit/647294ad7bfe421b031ae9464a60516f2714c7c1