Linking a WDNR3400 and DGND3300 through Powerline AV200 Adapter Kit

I have a WDNR3400 router connected to a BT Infinity modem [UK], serving as my main wireless hub. It is connected via AV200 powerline plugs to a DGND3300 router acting as a wifi range extender in a remote part of the house. The set up is roughly as follows:

Hub [WDNR3400]
DCHP routing on
IP address 192.168.1.1
IP range 192.168.2 - 200
Utilising 2.4GZ [ch11] SSID=Wifi1 and 5GHz[ch36] SSID=Wifi2 signals
Guest networks on
SSID broadcasting off

Slave [DGND3300]
DCHP routing off
IP address 192.168.1.201
Utilising 2.4GZ [ch5] SSID=Wifi1 and 5GHz[ch44] SSID=Wifi2 signals
SSID broadcasting on

The intention was to achieve relatively seamless switching between wifi networks with high demand devices using the 5GHz network and low demand on the 2.4GHz network. It is not working out that way and there are blackouts occurring where even though the devices are clearly switching from the weaker to stronger signal they are no internet connectivity.

I am not gifted with much IT expertise but am confused because this setup is replicating what was running perfectly before using the DGND3300 as the hub on a ADSL connection and a BT Homehub 2 router as the slave. The change has come about because I have upgraded from BT Broadband to BT Infinity.

Any help on the necessary settings on the routers to make this work better would be appreciated

Thanks

Sean