LAN routing goes down every day

[robotfishe]

Hi all, really at my wit's end and needing some help here.

A couple of months ago, my LAN - then running 23.7 - started going down every day or two at seemingly random times. I couldn't find anything in the logs to indicate what was wrong. I hooked up a monitor and used the CLI and tried pinging a few IPs. WAN addresses reachable, LAN ones not - both wired and wireless.

Thinking it might be a problem with the realtek NICs in my mini PC, I bought a used thin client and an Intel x540 card. Tried installing opnsense and carrying over my config; same issues. Tried a fresh install of 23.7, then a fresh install of 24.1; no luck. Changed out the switch, and the ethernet cable between the opnsense box and the switch. I even tried moving to pfsense and still had the same problem! I'm completely lost now - if it's not a software or hardware issue with the router, and it's not an issue with the switch, what could I possibly be dealing with?