Speed diff between ISP router and Asus RT86U router

[Sébastien GEOFFROY]

Hello,

I have an ISP router and a 1000mbps fiber connection.
When I connect my PC directly to the ISP router with a Cat 6A Ethernet cable, I get compliant data rates (960 Mbps down and 294 Mbps up).
I have an Asus RT86U router connected to ISP router (Cat 6A). From my Asus router, download speed does not exceed 460 Mbps.

How to explain this difference?

Thank you

 

[Sébastien GEOFFROY]

Just found than disabling QoS on Asus router fix speed issue.
W/O QoS : 900 mbps
W QoS: 430 mbps

Really strange

FW is latest AsusWRT Merlin

 

[CaptainSTX]

Really strange

Expected behavior. Enabling QOS disables some features including hardware acceleration features.