Last year I had a really weird problem with my home network. My server's network interface did not work well with my switch. For some reason, at some random time, my server was not reachable anymore. Dead. Could not ping and access over SSH.
In the IPMI Java console I did see this:
You can ignore the no space left on device error, it was not wart of the problem. The weirdest thing however was, that I could access the IPMI interface even though it was connected to the same switch.
I replaced the switch, network card, and cables but the problem was still present.
In order to get notified when this happens, I search for a monitoring tool and found uptimerobot. The free service will offer you a 5-minute interval check for up to 50 endpoints, neat.
If you self-host Home Assistant and make it available to the web, you now can know if your ISP is down or your server running Home Assistant has a problem.