Changing the layout of a Taxonomy Term Page
Thanks to @prkos, it turned out that the root of the problem was located inside the Bootstrap Sub-Theme.
Someone created a (hacky) template override for one specific content type in a generic manner. By renaming the file views-view-unformatted.html.twig to views-view-unformatted--SOME-CONTENT.html.twig it kept the override for the mentioned content item, but also made layouts of other, generic content types work as intended.