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
The german one is wrong
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?

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