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