120% same history here... First it was fine and then the network flooding.
I even tried with a USB-C NIC - it flooded the network even after I turned off the computer (power was still on the USB port) - only after unplugging the NIC the network recovered.
I've tried to install Windows 11 on the pc now.
Until further it has been running rock solid with a Virtualbox VM Ubuntu Server on top of Windows.
I've not been able to make it run proxmox stable.
Funny thing I can add to my problems.
I brought a USB-C to Gigabit network card. Reinstalled Proxmox and restored my Home Assistant. It still crashes as I wrote earlier.
Now comes the funny part.
When the computer was crashed/unresponsive I powered off the computer by force (holding power...
It seems my crashes are more often, when the Proxmox is under load.
I had it running without anything else than Proxmox, and it crashed after approximately 2 days.
When I run one or 2 machines on it, it crashes more.
I've got a PN51-E1 and have a lot of freezes as well. When the Proxmox freeze, the network port is overloading my switch/network. Only a power cycle works :(