@Tedd404 thanks very much for the advice. I've had a look and will forget and try and re-adopt them remotely if I can. I was hoping to be able to simply 'set-inform' on the APs to ask them to look for the WAN IP of the network where the controller is hosted because the devices are going to be located on a network that I don't have (and don't need) access to. Do you know if I get the devices back on the LAN where they were adopted if I can configure them so I can simply plug them in to a working network elsewhere and not have to run discovery etc on the remote network? All port forwarding is configured on the router, I have no hardware controller. Would entering my WAN in Settings > lots of clicks > Option 138 effectively set inform the host controller? Any advice very gratefully received.

  @Tedd404 thanks again for your help. I reset both devices and adopted them at a remote location, all working seamlessly.