[AC1900P] NAT loopback Slow speed when using ethernet

Hi,

I have a ASUS RT-AC1900P router with default ASUS firmware (3.0.0.4.384_45149).

NAT loopback "works". I connect to my DDNS : https://whatever.cooldns.org
My issue is that there's a big difference in term of speed between WiFi and Ethernet :

My NAS is connected to router is ethernet.

My PC or Mac is connected via...
- WiFi: same speed as if I was contacting the local LAN IP (approx 200 Mbps)
- Ethernet: slow speed, like if the packet were...

[AC1900P] NAT loopback Slow speed when using ethernet