Dynamic anchor image link not working

I got an anchor image on a layout page (NodeJS) with a dynamic link, which looks like this:
<a href="/shop/brand/{{brand_slug}}"></a>
The brand_slug is successfully retrieved from the SC, but the anchor link on the frontend looks like this and therefore doesn’t work:
/shop/brand/%7B%7Bbrand_slug_url%7D%7D

I tried removing the anchor image and inserting it again.
Checked if the routing script are on the layout page and if other routings work (which is the case).
Tried adding a click action (dyn. att.) to the image to use a Browser element’s GoTo function with the same url and that does work.

So it seems it’s just the anchor image link not getting published correctly on the frontend.

Any idea what could be causing this? Thanks for any help.