Using that great tool pingplotter only shows PL on the first hop and all the other hops are not affected - some googling tells me failure to return ICMP TTL-expired error packets on an ICMP ping packet with an expired TTL is not a real problem, as the destination is not affected.
Anyhow - will monitor but am running a few pingplotter traces and they're currently showing green on all hops which I suspect is good.
Urgh why can't networking be easier !
EDIT: Brilliant tool pingplotter, confirms that router is ignoring IGMP packets and showing "loss" at the first hop which is actually not loss at all https://www.pingman.com/kb/article/initial-hops-100-packet-loss-6.html
So now to monitor the rest of the hops and see what happens.
I also use this tool to monitor for line issues and where possibly the problem could be.