I did additinal test to reset the ONT but didn't fix the problem. It's pretty clear that the hardware is fine since it can achieve higher speed behind C4000, just doesn't work when directly connected...

@AdventureVia I just posted my own tests with AX11000, but the firmware speed test result from my AX is similar as yours. My main problem is my WiFi connection will have upload speed at 10Mbps.

Long story with a lot different setup test. 1. I have a gigabit fiber ONT directly connected with Ethernet cable 2. I have C4000 router from TP-link, tested speed with the included speed test from...