I'm experiencing the same thing. Texted back and forth for an hour showing correctable/uncorrectable errors and frequency and power levels for my modem. For some reason only 4/8 upstream channels are bonding. Usually get good pings, but have been getting bad packet loss upstream, this is apparent in game especially Unreal engine games that show network stats overlays. I've tried enabling options to extend power for upstreams and just power cycled my modem around an hour ago. This is an off and on issue which makes it super frustrating. I've got a netgear c6900 and dlink unmanaged switch, both are gigabit and my network card is gigabit as well. Lastly, I recently purchased all new Cat6 cables less than 3m in length. All my connections are wired.
I have a newer modem than you Jaeger I wonder what they will say about my experience?
