@Have you tried connecting directly to the ONT as suggested by@@pippincp in message3 to prove the bottleneck is the SH2?
Just as a matter of interest have you or an Openreach engineer tried changing the ethernet cable from ONT to Hub?
I can’t see it being the Ethernet cable at fault as they only connect at 10/100/1000. To get 500Mbps through it, it’s clearly connected at 1000Mbps.
@dave44Just because you can't see it doesn't rule it out as being the problem. It has been reported as a fix before.
ONT connected with supplied "RED" cable to SH2, from which "Yellow" cable is feeding directly my AIO PC...
Download speed 910 Mbps - 1.2 Gbps on Fast.com
Upload speed 95-113 Mbps on Fast.com
Ping 5 ms / 8 ms unloaded/loaded...
Obviously, Wifi is another story...
WiFi on less crowded channel ( 5 Ghz) directly on SH2 5: up to 350 Mbps download
WiFi on third party router (in separate setting behind SH2, connected by CAT 5E cable):
5 Ghz band (channel 64 in 80 Mhz channel width,for example): up to 450 Mbps dowload
5 Ghz higher band (channel 120/122 with 80 Mhz channel width, for example): up to 690 Mbps download.
All wifi somehow align upload speed approx 110 Mbps
For sure, it's possible to get maximum speed on wired connection, even with SH2
Unfortunately, WiFi part of SH2 will NEVER provide sufficient speeds, due as SH2 in general using only 4 (previously 3) sets of channels at 5 Ghz spectrum, and especially in urban areas, this is already really congested, and there will be plenty things,which will interfere with it.
Third-party routers could be solution, or, if (question is when - 2022? 2023?) wil be avilable SH3 with WiFi6 standard, might be solution...
Please to be aware, as some functions, like Digital Voice, or BT TV Box Pro Internet stream are unlikely to works with 3rd party routers.
To try PC directly connected to ONT is first way how to determine, if SH2 is problem, or not.
Also, PC's LAN card might be somehow bottleneck, or cable, if used older specs, or, even if there is wrong instalation...