Sorry I don’t have anything helpful to add other than a “me too”. I had this problem with a UPS years ago that would power down as soon as any comms was attached. I put it down to a faulty comms module (which was built in and not removable) and gave up. I hope you manage to figure it out

I might cop some flack but I use Cisco, they’re rock solid, last for years and just work with minimal issues and I’ve not run into problems with hardware under performing or firmware bugs like I have on others.

That said, Ubiquiti makes fantastic hardware, I believe Mikrotik does too.

You can absolutely buy open hardware that allows you to install custom switching OS; Dell and Mellanox make them as do many other manufacturers (I think even Facebook has a hardware switch, not that I’d buy it lol). One of the more common OS to install on them is Cumulus Linux and a lot of these use “spine leaf” topologies.