Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
Is this in The Roku Channel? Movies and TV shows offered there will come and go based on the contract that Roku has for providing the content. Yes, at times it seems strange that some seasons are available while others are not, but that's what they are contractually permitted to stream.
Will the missing seasons appear at a later time? We users have no way of knowing. It's completely under the control of Roku and the providers that offer the media for streaming. And even Roku can only stream what the providers offer, even if they'd like something else.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.