Fwiw i've had long running devices that just constantly ARP broadcast. Affects the local network only but if that's how you measure bandwidth you'll notice it.

Ie. Non stop "Who has IP/MAC address XYZ? tell ABC" ARP requests, then a second device see's the request for XYZ (which may not even exist on the network anymore!) and realizes it too doesn't know who XYZ is, so it too sends it's own broadcast. And on the cycle goes as devices constantly see others requesting knowledge of XYZ and triggering the request in a cycle.

Embedded devices are especially susceptible to doing this. You might not even notice, apart from a mild "my network feels slow" unless you inspect at network traffic closely. The worst part is these ARP storms basically require you to power down everything and power back up again. In the most classic engineer move the most effective way is to reboot the house. Ie. flip the switch at the fuse breaker and turn the house back on again. That turns all devices off and on again and causes what ever IP/MAC address confusion that triggered the storm to resolve.

Worth investigating for OP. Especially for home networks with a lot of devices. Home routers won't stop a broadcast storm and once it's going they don't stop. Happens more often than is discussed in my experience (i think people just don't notice that poorly programmed devices can do these cyclic and endless ARP requests)

I wouldn't trust flipping the fuse to the house because of thundering herd issues. When I restart my router I first disconnect all WiFi clients and unplug the Ethernet connections. Then I let it do its thing, download its mysterious updates, etc. Only when it's solidly online do I reconnect the clients one by one...