Your router is sending "echo requests" to the device at the other end of the line, and not receiving any answer:
Mon Mar 13 12:36:10 2017 daemon.info pppd[3918]: No response to 5 echo-requests
You may want to send more echo requests before giving up, or even disabling it completely, but then PPPoE will not restart the connection when it goes down. Have a look at the "keepalive" parameter in your configuration.