X11 forwarding over ssh only working with sudo
Regarding the hostname resetting, check if you have something like cloud-config installed and configured. It really messes up some stuff, you probably need to change some option like update_hostname or set_hostname.
Regarding the question, try adding the following to your sshd_config and restarting sshd.
X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost yes
AddressFamily inet