Extreme lag despite good internet, good computers, tethered connection, and close physical proximity

[azure flower]

Hello,

My brother and I have consistently been having connectivity issues with Factorio (and seemingly only Factorio). We have about 1 second freeze lag every 4 seconds, consistently spike to 254 ticks, almost get dropped from the game due to lag and so forth. Sometimes, we can't even connect to the game before timing out.

We've tried both of us hosting through Steam without a dedicated server. Lag persists regardless of host; it just affects the other person.

We live about 20 minutes from each other, we both have 200/200 internet speed and way overkill computers.

Any ideas what the cause might be?

Thanks for reading.

[scenic lily]

tbh that sounds like some device somewhere in the middle might be dropping packets, so not necessarily something you can fix. What you could try is connecting via IP or the server list instead of Steam.