I have a running support case with the latest v15 firmware not reliably working

I tried the latest 7.2.8.8 and this also gives the same result - the LG TV wired to the router cannot stream any of the streaming apps (Netflix, Apple TV, prime etc) and a wired MacBook speedtest drops to near zero. As soon as I revert to 7.2.6.31 full performance is restored on these wired endpoints. I've tried factory resetting and using the minimum configuration to get ISP connectivity and proved the issue is with wired connections to the router on all firmware since 7.2.6.31. Netgear Support even sent me a replacement RBR860 and this gave the same issue but worked fine once flashed back to 7.2.6.31. 

Has anyone else got an LG TV G4 OLED or MacBook M1 and tried it wired back to their RBR860 and tried to stream or run the speedtest app?

I've created the attached graphic to show all the troubleshooting and connectivity modes I have tried - it should now include v7.2.8.8 as also failing.

I believe my case has been closed as the suggested work around was to wirelessly connect the TV, which works but its not as seamless when streaming 4K as wired at peak times. My guess is there's a code change to the way the ethernet hardware is managed since 7.2.6.31 that shows on router wired endpoints when streaming - QoS, bridging, auto-negotiate or flow control, but sadly Orbi doesn't have any configuration parameters for the ethernet interfaces to tweak like QoS. 

BTW contrary to community guidance, I've been running the satellites on the newer firmware and now they are on 7.2.8.8 while the router is back on 7.2.6.31. All has been fine over the last 18 months with the satellites on newer firmware. I have tested with them all on the same firmware above 7.2.6.31 to prove this is not a factor.