For what it is worth:
I have nothing but challenges with the iOS and downloading from my plex server. Found an article on DNS rebinding that mentions that it needs be turned off. Update on new Downloads feature Topic number 4.
However, didn’t really want to disable it. But what I did do was add the IP address to the alternative hostname under the DNS rebinding check box. (Pfsense router)
Now I can download to the iOS devices.
