Wired Bandwidth issue on yellow port

Hi everyone.

For the story, I had a RBK50 V1 but after the satelitte has died after a bit less than 1 year, I've had a RBK50 V2 as a replacement unit. The first one was buggy and was rebooting randomly many times every hour. So the second replacement unit (brand new one) seems to work correctly, Router and Satelitte are running V 2.5.1.16.

But I'm experiencing a very strange issue.

My router is configured in access point mode.

The RBR50 is connected to my router (an Edgerouter X) via ethernet cable and my PC is connected to the second port of the RBR50.

I also have a NAS connected to the Edgerouter.

When the Edgerouter and the RBR50 are connected via the yellow port of the RBR50, my bandwidth between my NAS and my PC is limited to 70 MBytes/s. I've checked cables and everything, I can't increase the speed. But if I connect the RBR50 and the Edgerouter via another port (not the yellow one), the speed is OK at 112 MBytes/s.

Do you see where can be the problem ?

Thanks for your help