Just tried the Roku Channel on my Sharp TV. I couldn't find Good Morning World, so I just picked a random movie (Godzilla). I had no problem starting the movie, and also tried fast forward with no issues. Perhaps there was just a network hiccup when you tried it.
Dan Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.