Same here. My router was offline this morning and HA was unresponsive.
Even once LAN was back up, I still couldn’t access HA. Showing as offline
I had to use the CLI to get access to re-activate the network instance.
Once it was started I could get into HA and in Settings | System | Network
I could see my IP4 had been set to “Disabled” ?
Reset it back to DHCP (reserved IP) and it rebooted back up normally again
In case you’re wondering about the CLI commands
From HA > type:
login
nmcli
nmcli connection show
nmcli con edit "Supervisor eth0" # or whatever your HA instance is called
save
activate
quit
It should pop back up on the network allowing you to change the IPV4 settings back to DHCP again