I woke to an oddity. The lights hadn’t come on at 06:00 based on the light outside.
I checked the pihole and it indicated a crazy increase in DNS requests since about midnight. I initially worried it was an exfiltrating malware. However then on the pihole I noticed the massive increase was in requests to time.google.com (predominantly from the Google Home devices; you can see the change in the traffic once I unplugged them).
On checking the modem I realised it was a reaction to an internet outage – which as the pihole graph indicates, lasted for about 11 hours.