Stuck at ConnectingToGameserver

Hello.
We have set up PhotonServer on a local machine, opened all specified ports and shut off any and all firewalls and virus protection. When we attempt to connect to this server within the LAN, it connects fine. No issues.

However, when connecting over the internet using a public IP address, we get stuck with PhotonNetwork.connectionStateDetailed reporting ConnectingToGameserver.

We have verified that we have OnJoinedLobby fires, which is where we attempt to join or create a room. However, this does not happen and an error is thrown:

Client is not on Master Server or not yet ready to call operations. Wait for callback: OnJoinedLobby or ConnectedToMasterServer.

As I mentioned, OnJoinedLobby DOES fire, and it is in that callback that we attempt to create or join a room, but doing so is what throws the error.

As note: ConnectedToMasterServer never fires.

We have poured over our port setting double, triple and quadruple checking them for accuracy. The server runs fine if the game connects locally. What are we missing?