That's probably not an error. Detailed console logs and displays a lot of useless stuff. Just ignore that.
As for your friend trying to join you, you have to be inside a match first. And if UPnP still doesn't work for whatever reason, you can always port forward - https://plutonium.pw/docs/custom-games/#if-upnp-is-still-disabled-or-you-cant-connect-despite-it-being-enabled
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