Kwam dit nog tegen op UI site. Mss proberen waard.
Just WOW - I had the exact same issue: my ISP upgraded my connection to 1Gbps but I couldn't reach it through my USG. If I connected my laptop directly to the upstream connection, I saw the speed that I expected.
I tried this solution, just for the lolz, and YES, it worked. I switched the LAN cable from LAN1 to LAN2/WAN2 which wasn't even configured. Rebooted USG and waited until Unify Controller could see USG (but I didn't get any Internet). I then switched the cable back to LAN1 and rebooted.
And then I saw full speed!
I can only imagine that USG had to do some additional handshaking with the router upstream which it only did after this weird dance. I had rebooted my USG before I tried this, so that's not the issue.
But if anyone else has an issue like this, maybe worth trying also this trick.