@Solla-topee Not sure what you mean by "please check the Ethernet speed from the 850RE as well to see how much it is;" It is not connected via LAN / ethernet cable if this is the question. It is...

@Heinzipopeinzi I have updated Firmware. No effect.

several Speedtests executed, e.g. http://breitbandmessung.de (recommended by provider) Bandwidth on original Router: 209 MBit/s Bandwidth on TP-Link Repeater: 18,9 MBit/s ie behind the repeater its...