With the package installed:
* Icon is fuzzy/low-res
* It's the old sliders icon rather than the screwdriver/spanner icon.
Removing the package fixes this, but it shouldn't really cause the problem when installed.
Sorry, to be clear, by "the package" I mean gnome-icon-theme-legacy
Per https://gitlab.gnome.org/GNOME/gnome-control-center/issues/3, the gtk-missing-image icon is useful, but that is in the -legacy package at the moment.
Maybe just remove the gnome-control-center categories icon from that package per comment 3 there?
Thanks, I dropped them in https://src.fedoraproject.org/rpms/gnome-icon-theme/c/416754015c9469e732a819e8bb27a81a1a85e29e just now
gnome-icon-theme-3.12.0-9.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-894bd8ae9a
gnome-icon-theme-3.12.0-9.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.