Every day at the same time, my internet dies for 1 minute. How do I investigate?

3:40pm every day my wifi loses internet access. My devices remain connected to the network, but all traffic dies. Almost exactly 1 minute later everything is resumed. I have no idea what the cause could be.

How could I begin investigating this? I have a spare Raspberry Pi and and old Android phone at my disposal, and some programming competency.

If your devices are kept connected this means that your wifi and router are still active, probably the issue somewhere behind your router, either a connection or provider. But due to exact timing it's likely something on the provider's side and not just some connection issue. I would personally start with contacting them to investigate.

You might also check the router's logs for that time, perhaps there's something useful information.

Do you have xfinity by any chance? And are you using their x1 combination modem/router in bridge mode with custom (non-comcast) DNS settings?

Because the exact same thing was happening to me at the exact same time. I’m no networking expert but when I checked the logs it seemed that every day Comcast would try to “fix” my (not broken) DNS settings. I had been using mullvad DNS and open DNS as backup but since switching to nextDNS the issue has stopped.

I don’t know enough about networking or DNS to offer any explanation as to why.

Get better hardware and software that properly reports error messages instead of hiding them.

Launch ´mtr google.com’ on one of your devices (preferably connected via Ethernet to your router) a few minutes before the cut off, and watch what happens when the cut occurs. It will show you exactly which equipment on the route starts dropping.

Although I suspect your ISP has a 24h lease and your modem renegociates at 3:40 everyday