I am going to bring this piece of ... not correctly working hardware back!

I have installed alternative Firmware TomatoUSB on my Asus RT-AC66U. Nothing changed. Than I tried channel 100 and above. Also not working. Next thing I tried is setting the "Access Point + WDS" mode...

Model : RE450 Hardware Version : V 1 Firmware Version : EU Firmware 1.0.0 Build 20160727 Build 63203 ISP : Hallo, I have bought the RE450 Repeater, I can connect 2,4 and 5 GHz Wifi with my ASUS...