Continually getting "disconnected from server" and booted to the main menu without any apparent cause.

[Betrix5068]

My Ethernet is both quite fast and reliable, and I don't have any issues with other games, so I'm at a loss at to what the probable cause is. I checked my firewall and that shouldn't be blocking things, and I'm not using a VPN or other service which would cause network issues, so I'm clueless.