Good thing to know it was just a wrong WAN IP problem 
by the way, with “strict network settings” I was referring to Atlas settings. but that could also be a problem from the hotspot, router, proxy, vpn, etc, yet they mostly cause “connection timeout” error 
in your case, you were connecting but refused due to strict IP access.
one more thing about my “PS:” in my post above. it is about the IP change of the database server itself. it is a different thing than the IP change after hotspot/router restart or vpn/proxy changes.