@acesxi 

If it is the Deco wired to the modem, then the red LED is saying it is not getting an internet connection. It could be simply the Ethernet cable so I would swap that out and see if the connection still drops. Another thing to potentially try is to use the other LAN port. 

@Tony hi, I doubt that it is the modem because I have a laptop wired directly to the modem as well and it is not losing connection, and also when the Deco is manually restarted, the internet comes back after a few mins without touching the modem. Will try your other suggestions though and will get back here to report after 1-2 weeks.