@Clive_A @ChrissNeo Thanks both for your replies. I found the issue - it was the controller activating the IDS/IPS setting. IDS/IPS was the reason for the reduced performance. The throughput rates...

@Woodae Update: I forgot the gateway from the controller and reset to factory settings. Setting up the internet service, DHCP and the same service configurations as I had above. Speed test delivered...

@Camfj141 I have the same issue - did you ever find a solution? My gateway (ER7412-M2 v1.20) is running latest firmware and configured like this: Connection type PPPoE IP address from ISP MTU and MRU...