If gnome-control-center is the setting app you are referring to, you can try launching it from the terminal and checking to see if any output is displayed in the terminal that would tell you where to look. You can just open a terminal and type gnome-control-center.
Of course, if you installed any software without updating your system, make sure you update as that can break your system on any arch-based distro.
I can run only with sudo the gnome-control-center app. It pops for 2 seconds and then it’s gone. In the terminal I get all this:
(gnome-control-center:4794): cc-wwan-panel-WARNING **: 01:14:18.400: Error connecting to ModemManager: Error calling StartServiceByName for org.freedesktop.ModemManager1: Unit dbus-org.freedesktop.ModemManager1.service not found.
(gnome-control-center:4794): dconf-WARNING **: 01:14:18.405: failed to commit changes to dconf: Error spawning command line “dbus-launch --autolaunch=50e410170a0742d28b6ae255f3c827e6 --binary-syntax --close-stderr”: Child process exited with code 1
Error creating rfkill proxy: (null)
To not have to redo all the settings, alternatively you can just reset the gnome-control-center settings in dconf-editor by changing the last-panel key, unfortunately I don’t even suspect what might be causing this problem, the fact is that the last panel will always start and if it is having problems, the settings center will not open.