This message suddenly appears on ONLY one of 2 identical ROKUs that were purchased at the same time! I also have 3 other different ROKUs that are all older/lesser models — the message appears on only the oldest and slowest of these. What is going on?!?!
First, we'd need to know what model Roku players you have, and which is giving the message. Not the name, the model number.
Not every channel in the Roku channel store will work on all devices. That is not something that Roku controls. It is under the sole control of the channel developer, in this case Sling. Are they dropping support for some players? Certainly a possibility, but only Sling can answer that question.