Sorry for the late reply.

For anyone interested in Minisforum releasing a bios fix for this issue, I'd recommend you email support@minisforum.com and voice your interest in this.

Hopefully they will not state a fix is not possible, but if they do, kindly point them to the following:
https://www.asrockind.com/en-gb/index.php?route=newsblog/faq&faq_id=91

This is a competitor's board with an AMI bios and the same i226-LM chip. I am not a bios expert by any means (it probably is not as simple as this sounds), but that link did seem to get them to consider the possibility.

Thank you so much for providing this information. Ever since Xfinity did their infrastructure upgrade in my area I would have intermittent connectivity with one of my WAN's. Currently, I am running two WANS (both Xfinity) and have them in a load balance configuration. When I initially set this up in Pfsense everything was working fine. After the Xfinity upgrade the non-default WAN would intermittently lose connectivity and show as 100% packet loss. The weird thing about this one it would only drop the non-default gateway. The default gateway was always up. So if I swapped the default, the packet loss would also follow the other non-default gateway. So I knew this wasn't a hardware problem, For the past 4 months I have been trying numerous troubleshooting steps including a complete reconfigure of my pfsense setup from scratch and nothing worked, at least not until I added 'supersede dhcp-server-identifier 255.255.255.255' under "Option Modifiers"

Thanks again, this saved my sanity. :)

Re: PFsense random loss of WAN gateway

I just wanted to add my thanks!

I have a Telia Fiber connection and it would lose WAN every six hours. Turns out that the Telia DHCP server only allows a limited number of renewals after which it demands a broadcast again.

The above option to always broadcast works fine.

It took me several month to find this solution! Thanks again!

So you plan to have two connections between the modem and the existing router and you want to put the SG-2100 in one of them?

I thing we might need a diagram here.

Steve

SOLVED:

I wish I knew why for those that follow after. I changed a few things at once so I'm not sure if one of or combination of them was responsible or the fix.

I turned off TCP/IP on the WAN NIC. I rebooted the modem and router at the same time with cables connected.

Yeah what confused me the most is that router->internet was testing at 750mbps+ with speedtest-cli, and desktop to router (through the same switch I'm normally connected through) was testing at 400+mbps (when downloading a dummy 1GB zip file I put in the web dir on the router... and it probably could have ramped up faster if it hadn't yanked the entire file in ~20 seconds).

That's what got me looking at the router configuration itself, because obviously the router->internet connection was fine, and the PC->router connection was fine -- so it had to be something on the router itself that was bottlenecking things.