Sorry to be that license guy, I'm a little bit confused by the Oxygen icon theme licensing.
It says on the spyder license file that it's Create Commons BY-SA license but https://github.com/KDE/oxygen-icons/blob/master/COPYING shows LGPL-3.0

Also the Crystal Project Icons seems to be LGPL-3.0 after hunting around, seems a bit abandoned, so not 100%, the website listed is borked, other sites suggest LGPL (no version listed).

As for https://preloaders.net/en/terms_of_use I'm not sure how that's licensed.

I will add LGPL-3.0 then all bases are covered. The KDE wikis are CC-BY-SA licensed, so it could be possible that the license of other KDE projects like oxygen were different at the time the assets were copied/forked to Spyder. With regards to the preloaders site, it states quite clearly: "All GIF and APNG images marked as "Free" are completely free to use in all projects (web and desktop applications, freeware), with the exception of web-site and application templates with commercial basis (e.g. online store template). You are encouraged, but NOT obligated to place any reference to https://preloaders.net web-site to use it`s content in any personal projects and applications". This shouldn't be an issue whatsoever, Spyder doesn't even need to reference them if they didn't want to. I'm fairly certain that once this is submitted Solus will be the first distro to fully document all the licenses of Spyder, the only other one that I could find that had anything other the just MIT was Ubuntu/Debian, and their list was by no means complete.

@Justin, is this (and D1007) ready to go in?