Hi Guido,
Thanks for pointing out my mistake. What a sh*tshow... there was an underlying line under the secondary road tagged "political boundary" (that probably no one gives a sh*t about) but also carrying a "highway"tag and of course being connected to a lot of different other stuff (crossing, etc). So deleting this line has been hellish.

Hope it's fixed, please confirm.

p/s. had to look for "duplicated edges" also since I had no clue what it was.
Best,
Lorax