Good morning,
Since I made this subject, I have not come back because my router always reboots but in a “bearable” way, i.e. once a day. I ended up letting Swisscom customer service down since they couldn’t solve the problem (I’m not blaming them, I can understand that it’s complicated) and after all 1 reboot per day is not death even if it sometimes happens badly.
But today I’m on the 3rd reboot between 4:00 p.m. and 9:00 p.m., so I came back to look here. So I’m going to try to disable IPv6 as FM33 suggests. It’s easy and costs nothing so you might as well give it a try.
Thanks for the tip in any case, I’ll come back and tell you it works for me. 🙂