Networking problems when both wifi and ethernet are active


I have what I think is a networking problem with my setup. I have a laptop connected to a thunderbolt dock plugged into ethernet & at the same time to the WiFi.

The problem is that when both networks (different ips) are available to my laptop connection is painfully slow. If I disable one of them ( I primarily tested this with WiFi disabled as it made more sense, but I can notice the difference with the cable connection unplugged, as well ) everything is back to normal.

I’ve seen some topics mentioning DNS related problems with the notorious /etc/resolv.conf, but it does not seem to affect in any way with my configuration. Also as I am not that sure what is the problem & not so familiar with nixos, I am looking forward to your suggestions.

Laptop: Lenovo Thinkpad T480
Thunderbolt dock: Lenovo ThinkPad Thunderbolt 3, Dock Gen 2
NixOS: 23.11

Thank you in advance!