@Graham307 The issue seemed indeed to be related to DHCP, the range extender is using the same subnet as the main router and it apparently gets the same ip (192.168.x.1). The issue as far as I could...

@David-TP I have the same issue with a WA860RE_V6 connected to a Fritz!Box 7510. When the repeater is connected, the Fritzbox seems to still be online but most servers can't be reached. Other divices...