The ue0 link state changed to down means according to OPN, it can no longer use the link, so all communication via it will fail, as you have experienced.This is why these devices are not suitable for a network appliance.
have you troubleshot it and confirmed it is OPN that is at fault?
what I mean is, whether the problem is the opn software or the hardware interaction with it.you'd want to verify if possible. Any clues in dmesg ?Do you have the option to add a pcie card to this machine? If yes, an intel based nic of two ports would be good.
without trying to set wrong expectations, some people do use realteks without problem, to a point.You might want to try to have OPN use the vendor driver instead of the freebsd built in.I can't search at present but search the forum for realtek driver, realtek module, realtek vendor, etc.Only good if you can keep a connection stable enough to work with the system.You do have another, non realtek nic, right? I guess there is a bult in nic, for WAN, if this is for LAN?If yes, then you might need to work with that as LAN initially.
Only read the thread diagonally - so could have missed something.Disclaimer aside, I have a few questions:Did you check in BIOS or any weird power management related settings ?Were cables changed, replaced, and did you confirm there aren't any speed port negotiation issues ? You can set the NICs to 1GB full duplex on both sides.Was the os-realtek-re driver installed ?