IP is not pinging, but does respond in a traceroute, but that seems not to be the end of the journey, as it tries to continue and gives host not responding but for the same IP address as previous hop.
Can you confirm it is Openreach FTTC modem to Asus router and the FTTC modem is not a hacked model, i.e. as supplied by openreach. It is possible this is a bug in the Asus PPPoE stack, as someone has reported low throughput on a high spec asus router as in it is handling data twice.