@Hank21 

Thanks very much for the reply.

In my case the clients in question were joined to subnets other than LAN/default native. Therefore, when the Config menu is accessed the Network dropdown is not empty as in your screenshot. In my case the clients Config menu was pre-populated with IOT (or another appropriate Network). At that point it looked like I could key in an IP address appropriate to that Network/subnet and Apply. However, the masking/error checking on the IP address was apparently still set on the LAN subnet and therefore generated an error when keying an IP address for the Network which was displayed in the drop down.

The solution to allow the correct IP to be entered was select any other Network, reselect for the correct Network (which was originally displayed), and then the masking/error checking on the IP address is apparently updated to the proper subnet and the IP address in that subnet can be applied.

Thanks again for your reply.