Unfortunately, there are no specific statistics that indicate who caused the connectivity error. I wish we would, and perhaps that feature can be tackled in the future somehow. If you can share the logs related to the issue, it may help identify which player was involved. I know that certain countries have difficulties connecting to us, and the average user usually has no idea how to fix that. They just keep trying until it works, and reach out to the mods/technical support after they got annoyed enough by the penalty system. (Solution for those cases is mostly: use a VPN) The new ice adapter is WIP and looks promising so far. There is no ETA, but work is ongoing. Hopefully it will tackle those connectivity issues more gracefully. But it will not be a "magic fix" for everything. My understanding of this subject is limited, because the architecture is extremely complicated. @nemir said in "You have caused a matchmaking error": maybe about ten percent of the time You are exactly right with that observation. There is a ~10% connectivity failure rate in the 1on1 queue. Which is relatively low, when 90% of the started games can be played.

A project based on copyright infringement thinks about copyright. That's strong.

504 means you were able to talk to api.faforever.com but it wasn’t able to reach the backend service. So the fact that it started working again after you flushed your firewall rules is just a coincidence. Just noting that in case someone finds this in the future and thinks that if they get a 504 error they can fix it by flushing firewall rules. You can’t. Just wait a bit and try again or notify the server admins.

Checking "allow ICE adapter to use IP6" and "force relay connection" solved it for me. However, I do have some lag issues now.