Then 0.4 or 0.5 or 0.253 or anything that isn’t the same as the router’s address or in its DHCP pool. Or shorten the LAN subnet mask on the router by one bit so the 1.x addresses are included in the subnet (though you’ll need to restart all your equipment after for that to fully take). You need to pick an address that the router recognizes as being on the LAN subnet.

Change it to 0.3.

Did something get plugged in that connected switch 1 and 2 directly, i.e. other than through the router’s switch? If you unplug one of the switches from the router does everything, including the stuff on the unplugged switch, start to work?

I have seen your symptom when switches not running STP are connected in a loop. Since ethernet loops never stop shutting everything down is the only fix.

If it has 2 interfaces, say Ethernet and WiFi, it will have two different MAC addresses, one for each. I guess they only wrote one on the box?

A very long time ago I worked for a US telephone company helping to operate their Internet service. One day we had an outage that took out a bunch of backbone circuits in the northeast (that we thought were diversely routed but weren’t). The problem was in West Orange, New Jersey. Someone had cut out and taken a big chunk of 96 strand fiber optic cable where it came out of the ground and crossed a ravine attached to the bottom of a railway bridge. Apparently they thought it was copper, which has value as scrap, and were probably very disappointed they did all that work for something that had no value.

So I’m going to guess what you are seeing might be the result of someone starting to rip out a length of copper cable but stopping when they realized it wasn’t. Maybe putting a sign saying “This is fiber optic cable” on the cable would help.