I'm having similar issues. 1gbit service. 1-5% packet loss (upload only downloads are fine (solid 0%). area: south hertfordshire.
hub 5 reboots help. i rebooted tonight and its down to 0.3% loss (even with a lowly pubg packet loss test of 130p/s). like you i have other routers but i left the hub in router mode (mostly through the hell that was modem mode on the puma chip on hub4) and it gives me a nice dmz to put web facing things on with an internal router handling wifi and lan protection. double nat isnt the cause as packetloss minimises on hub5 reboots, but i should really test that theory before jumping ship.
i really cba to go through the fanfare of support calls to fix it and my contracts up in 2 months as well. 1gbit is great, but not worth the PL in 1st person gaming. i "think" im lucky enough to have a g.fast enabled hub for 300mbit FTTC, but i'd take a solid 60-80mbit/s. I must give some of that cat 9 a go, that'll probably sort it out instantly, my lowly cat5e just cant keep up 😉 heh.
