Linux Ubuntu 16.04 how to solve the problem with the periodic loss of wired Internet connection?

Question

linux

Hello, I have a problem with Linux. I describe the topology:
The computer is connected to the router via a wired connection and is used as a server. For two years, Windows Server has been installed on it and there have been no connection problems.
The computer is displayed within the local network to its members and has access to the Internet.
After installing Ubuntu 16.04, the Internet connection drops intermittently in the range from one day to a week, however, members of the local network still see this computer.
Disabling ipv6 helped to delay the drop in the Internet connection (feels like).
The computer is forbidden to go into sleep mode, but in case of sleep mode, a script was set to reconnect.
To return the network, you have to disconnect and reconnect to the Internet through the manager.
Tell me where to start looking for a solution to the problem. What logs should be looked at and what should be done?