[Justkidding]

Hi everybody,

my Amazon Fire TV Stick 4k is giving me a hard time... maybe you guys have an idea.
I've connected my Stick with the Ugreen USB 3.0 Ethernet Adapter https://www.amazon.de/gp/product/B00V9XS...UTF8&psc=1 and an USB OTG Cable https://www.amazon.de/gp/product/B00V9XS...UTF8&psc=1 .
I've plugged the ethernet cable into the Ugreen adapter as well as an ethernet port in my ASUS RT-AC66U router. The ASUS is working as a WiFi-Repeater. The WiFi is coming from a mesh network consisting of a Fritzbox 6490 and a Fritzbox Repeater 1750E.
So now you roughly know my setup.

Now to my problem: 
When I plug one side of an ethernet cable into the ASUS router and the other side of the cable into my laptop I get transfer speeds bigger than 100 MBit/s (approx. 125 Mbit/s).
But when I plug the same ethernet cable into the Ugreen Adapter I only get transfer speeds of about 42 Mbit/s with the fire tv stick. The stick is not connected to a wireless network - only with the ethernet cable. 
I am using the exact same port of the Asus Router and also the exact same ethernet cable.
Do you have any idea what could cause this big difference of transfer speeds between the laptop and the fire tv stick?

Any help is really appreciated as I really have no idea...