@traumflug Thank you for getting back to me.
Some of the non-working categories are named "Kabler, stik og adapter>Multistik>24 pol Harting - Ilme", " Kabler, stik og adapter>Multistik>4 pol Harting - Ilme" and things like it. So no non-English characters I'm afraid. But categories like " Kabler, stik og adapter>Kabler>Kabler Til Strøm>Færdig Combikabler" with non-English characters work perfectly.
@musicmaster I have no issue clicking on the pictures to enlarge them, I am sorry you had problems though. The data in the pictures can be summed up as follows:
Two categories with the same parent categories, one producing perfectly reasonable SEO URLs, the other does not. Same type of category, same parents, no visible reason why.
As for the other image, it had my rewrite rules. They are as follows:
Route to items: {rewrite}
Route to category: {rewrite}
Route to category with "Selectedfilter": {rewrite}/filter{selectedfilters}
Route to supplier: supplier/{rewrite}
Route to manufacturer: manufacturer/{rewrite}
Route to CMS page: content/{rewrite}
Route to CMS category: content/category/{rewrite}
I have been unable to figure out any commom denominator for why these don't work - in the category itself, I see no differing variables between a working and a non-working category.