Named locations can't have a private IP range, look at https://docs.microsoft.com/en-us/azure/active-directory/conditional-access/location-condit ion
"User IP address The IP address that is used in policy evaluation is the public IP address of the user. For devices on a private network, this IP address is not the client IP of the user’s device on the intranet, it is the address used by the network to connect to the public internet."