After 6 weeks away, I've come home to all my smarthome tech working fine.
Except #HomeAssistant!
I can get into into its virsh shell, it appears to be updated and running. It is advertising an IP, which I can see on my router, but none of the apps/web will connect to it.
A reboot hasn't fixed it either. Oh well, that's what weekends are for, I guess…