I can also confirm that using generic windows drivers worked for me as well. I’m nearly in the exact same situation as you were. Fresh Win11 install, an MSI motherboard with a RealTek network card, and the latest driver installed.
I had tried everything to fix it myself and nothing was working. Firewalls, port forwarding, run as admin, file verify, Windows exclusions, VPN, network sharing from another PC,… None of it worked.
The PC that had the issues was working on Last Epoch flawlessly before my Win11 upgrade, but I wasn’t using the latest drivers when I was using Win10. I also had another computer running LE, (doing co-op with the wife) and it was running a fresh Win11 install as well, but it never disconnected. So, I had two PCs on the same network, with fresh Win11 installs, and only one of them was disconnecting repeatedly.
The working PC has an Intel card for wired and a MediaTek card for wireless. Both worked without issues on the latest drivers.
The PC that had constant disconnects when switching zones, loading dungeons, or monoliths had the RealTek network card with the latest drivers. Side note - I was able to reproduce the connection issues on another PCIe network card I slotted in with the latest drivers as well. This problem is definitely linked to RealTek cards and their drivers.
I completely uninstalled the latest RealTek drivers and had Windows replace it with their generic driver. I played for hours last night in multiplayer with 0 issues. LOVE IT.
If there are others out there who have tried everything else, I would implore you to try this regardless of what network card you have and DEFINITELY do this if you have a RealTek network card.
R.I.P. all the keys I wasted throughout this week testing solutions to resolve this issue, haha!
Good luck all, I hope I was able to help someone out there. I know MightyNicko’s post helped me a ton. Thank you!