[civiloid]

I think about these headaches as extra fun :)

But about your problem - cards manage to negotiate 5 Gbps, or even negotiation fails? If it's the latter, then it might be cables.

Overall, for me, it works to simplify the network as much as possible and first achieve results on a direct connection to the router when it's nearby and then add more and more.

Oh, and also measure as much as possible (that's why I'm sad about the state of system metrics on OSX, for example)