There are quite a few locations they store their information under root, but almost all of them store users configuration files in sub-folders in your /home/USERNAME directory. within it, most have your settings in the .config (a hidden) folder, other files like extras you download from the internet either there, and under .user/share, .local like icon themes, color pallets for graphics apps, but it’s not all that cut and dry, but very most often in your /home/user folder somewhere. If you delete one, which sometimes can fix a problem they “Regenerate” a copy of the one in root back to your user folder sans your customization’s. With them in users home folders, not only can every user have their own settings where they have permission to access them, but because it’s obviously great for not loosing settings every time apps or the OS get updates, they don’t get removed on uninstalling apps either unless you explicitly say to do so… which all of those things were always a horrific nightmare in Windows where you didn’t have an app store (still not where you get everything), and had to get everything from all over the freaking internet and spend days, weeks, even months getting things back to how you preferred them!!! Oh did that make me mad!!! 
Well, although it can happen that issues arise just by passage of time, it’s rare, and the fixes are often way easier to apply than a full reinstall, even with the OS itself, and that too is a Windows thing: Self destruction over time. So many people are used to doing full reinstalls for being used to Windows, and having no access nor say over proprietary software you cannot just delete, add, or change a line in a few or just a single text file which .config and many (Most) files are in Linux. So, way too many people suggest to do it, but it’s not necessary, and only easier if you absolutely need a quicker solution than searching the web for answers but it may not even fix any new problems, as you have reinstalled a few times already lately an it hasn’t worked. Reinstalling the whole OS if it’s an app is wasted time, and if it’s related to a bug that is being worked on that cannot easily be fixed or worked around, a fresh install of anything won’t fix it until the bug fix is released and ends up applied with an update.
I have had many bugs that were not so bad I couldn’t get the important stuff done, and put off looking for a solution and forgot all about it, then used the app and it just disappeared which is when I remember it, and it’s for having been fixed already and applied in an update. Arch, as well as KDE, are known for fixing stuff pretty quick, I can’t speak for XFCE though. Now I often don’t even bother unless its important because it can be more work to look for a solution than just wait. Only if it’s bad, and important do I look harder for solutions.
Great places to find help are first at the developers website, forum, bug trackers and Git pages, next a general web search: I set my search engine to find results for only a week if it happened during an update and I know the program was updated, for a month if it happened more recently between uses of the app, and a year only if I can’t find any newer results, or the program hasn’t been changed much for a long time. If that doesn’t work out, this forum right here, the Arch wiki, in the apps page on the AUR if it’s from there, as there are related notes by users posted there, and a tech site I love “Stack Exchange” where some serious tech people hang out that can often help troubleshoot things in great detail, and there’s lots of them with so much knowledge its often quick and painless, and you will always learn something. I’m sure there are others good places.
I don’t like the Ubuntu and most distro’s based on it sites even if always on top of a search: it’s a Debian, not arch based distro, so although many problems will be the same, they can be totally unrelated, and since it’s one of the first distro’s people try, its way more likely they are asking all the wrong questions and use poor descriptions of problems, and it makes it much harder to find the right one, among so many that aren’t even bugs or actual problems, but user error. Add to that there is a lot of “The blind leading the blind” there.
You are here now so in a recommended place, and I’m sure with a more detailed description of what is actually happening, you can narrow it down to something more specific, and ask a more precise question, and in a more appropriate section, of this forum.