It's sometime helpful to compare config files on different machines. Here is a one liner that can do it:
diff /etc/hosts <(ssh hydrogen "/etc/hosts")
This is my goto for checking whether my computers have the same packages install
diff <(pacman -Q) <(ssh kate "pacman -Q")
Even better is watching it while you change
watch 'bash -c "diff <(pacman -Q) <(ssh kate \"pacman -Q\")"'