This night (around 02:50) my Internet was dropped on my Deco M9 system. 

- rebooted. Still could not connect to internet. (Internal network works)

- unplugged power cable and restarted. Still could not connect.

- called ISP who sent over a team around lunch time. They were checking all cabling from optical access to apartment. They connected their own router which worked. Reconnected the Deco M9. Still no internet on  Deco.

continued myself after work.

- again all kind of reboots.

- factory reset and set it up from scratch. No internet

- factory reset on my other Deco and setting it up as main router. No internet.

- called ISP asking them to change from Dynamic IP to static. Factory reset and static IP. Still Deco can not connect.

- called ISP again, who did all resets they could from their side. Still no internet

- spent about one hour on the phone with the technician, trying all kind of restarts, switching back and forward between dynamic and static.

What did I miss !? How can it stop working by itself middle of the night ? Any good ideas what to try next ?

My Deco system have been up and running since November.

Tomorrow evening I will pass by my storage and pick up my “old” Netgear Nethawk and try to reconnect it to the network. If that one works, did my two M9 suddenly transfer into paperweights ?