I want to echo that 10G NICs do indeed seem to break Factorio Multiplayer. I was having Invalid Packet Type errors before swapping over to my 1G - all fixed. I was troubleshooting with my laptop first, similar to you, wondering why it was connecting just fine, even if I used the same hard-line as my...

I'm absolutely baffled by the Developer response to all of these multiplayer threads. It seems to be an area where they lack detailed knowledge, and it's a niche enough issue to not throw the community into fits. Maybe that's a good enough excuse, but I'm turned off every time I find another thread ...