I was hopeful Roku fixed the app with their latest update, however @Mike6377 now Roku has apparently "fixed" it so it will not find the device(s) until after it has verified the IP range. It started being able to connect again with your workaround. Still no private listening.
IP address shows in range specified, yet "not supported".
Agreed, why is this still an issue after all this time? The timing "solution" doesn't appear to be an option for me. I am still setting it up. It doesn't even seem to try to scan before telling me my 10.x.x.x address is invalid.