You've reported to German support? The problem is bluescreen will appear on the second computer after logging in for a while when someone has already logged in from another computer? It just happens...

With Qos, cannot cap specific download/upload speed for devices. That can be achieved on router that support bandwidth control.

that seems to be a serious problem. I would say contact Tplink support directly. If the problem occurs recently, maybe you can reset the router

does the connection drop on your gaming console? or it's very slow? from the screenshots that you sent, ping through WiFi connection is much higher than LAN connection, I think there might be...

There is not USB printer controller for MAC 10.13 yet. I learned from Tplink that it will be released soon, maybe this month

Nowadays they are not allowed to change region. it's either EU or US version.