gateway.find_server_process takes the last command-line argument of a running RLBotServer as its socket port:

https://github.com/RLBot/python-interface/blob/8a0850f/rlbot/utils/gateway.py#L80

port = int(proc.cmdline()[-1])

That holds when the interface launches the server itself (RLBotServer <port>), but core accepts a second argument, the game port (RLBotServer [socketsPort] [gamePort], see RLBotCS/Main.cs). If the server was started by hand with both:

RLBotServer.exe 23234 23233

then find_server_process("RLBotServer.exe") returns port 23233, so MatchManager connects to the game port, not the socket port.

A non-numeric last argument also makes the int() call fail. The process is then skipped as if no server were running, and ensure_server_started raises FileNotFoundError. We ran into this while testing an extra server flag locally.

Suggested fix: read the socket port from the first argument after the executable (cmdline()[1]), which is where core parses it, and fall back to the default port if it isn't numeric.

Found with rlbot 2.0.0b56 on Windows.