Different structure of hreflang links in head

Hello dear balbooa team,
we're experiencing an issue with a multilingual blog:
In the head the hreflang links do have a different and partially wrong structure depending on which language I am currently viewing.

Looking at a site in german

The english one - correctly - is
sitename.com/en/blogcategory/blogtitle
The german one is wrong
sitename.com/de/blogtitle
This site does not exist and results in a 404.

When switching to the english site the german one is right (sitename.com/de/blogcategory/blogtitle) and the english one is incorrect (sitename.com/en/blogtitle)

All blog categories are linked between languages, and so are the single blog posts.
Where did we go wrong to cause this?

Replies are visible only to logged in members with an active subscription.