I've created an archive and tried to make a category filter at the top of the page, they used to be there, now they're gone and I'm not sure what have changed.
I've uploaded some images, I'm not sure what information to give.
In the screenshot "wp archive query filter" there is a pink warning text.
This refers to how you cannot include taxonomy filters on a taxonomy archive (or, more specifically, you cannot include a filter for the same taxonomy as the taxonomy archive).
But your title suggests that this custom archive with taxonomy filter is used for the blog archive and the filter is not displaying there, is that correct?
Yes that is correct 🙂
See the blog archive here hidden link
It makes sense to me now why it wouldn't show the filter when looking at a category archive, but looking at the blog, author, month etc. archives, it's not showing either.
I've deactivated the taxonomy "categories"(Kategorier) for this archive.
I may need to take a copy to install locally to do some testing, unless you have a staging site you can share access to.
Let me mark your next reply as private so that I can get log-in credentials from you—you may want to create a temporary admin user for me to use that you can later delete. And be sure to have a current backup of your site.