No tracking on offer proposition links

We have created a custom html rendering function for offers.

Links in the rendered html does for some reason not get tracked (neither click tracking nor proposition tracking).

The offer html is injected in an email using content manager. Other links in the email are tracked.

When we inject offer html as "unrendered" raw html the links get tracked.

The reason for the custom html rendering is usability for the marketing staff managing the offers.

Fields are presented in the offer in a similair way as the content manager and the rendering function will make the html into the same structure used in the content manager.

Notable is that if a link is edited into a text in the offer (ie written manually as <a href="...) then that link is getting tracked. But the rendered links on image and button are not getting tracked. 

After some research and testing it seems like the tracking does not work when run through a function that adds utm properties to the link. Or even worse it works only when running the function on the textpart with a url (or several urls) as part of the text but it does not work when just running the url.

AND it does not work when I create a static string identical to the text with a url (that works) and run that through the function.

The content attributes in the schema of offers seem to be duplicated with _jst as suffix. The original url attribute is used (Destination URL (view/trackedUrls/url) No) but the text part that works is custom (view/mainText). Can this somehow have an effect on the tracking behavior?