Router not allocating IP address to Develo extender

[#1]

I'm not sure what has gone wrong or how to fix it but my Plusnet router is not recognising my Develo network extended.  The computer at the far end of the extender is showing as connected/enabled to the LAN but no internet connection.  Its showing a 10.x.x.x IP address at the moment.  The Develo plug is also not showing on the Network Page under Advanced settings.  

Do I need to give the router a big kick or is there something else I should being doing?

Thanks

Simon

[#2]

Is this a single WiFi range extender or pair that communicate over your mains wiring?

[#3]

When I used a pair of homeplugs, they didn't get allocated an IP address as communication only required the MAC addresses. The PC did get allocated a DHCP address in the same way as if the homeplugs had been replaced with ethernet cable.

[#4]

I'm using Develo Due 500 plugs and previous things seemed to be working OK.  Now the plugs are shown as connected but upon looking at the connection settings computer is not being given internet access.