You didnt state your Roku model # or firmware version: Settings/System/About
You also didnt state the specific error/error message displayed for the Disney channel, and its not clear when the message occurs (first you said when it starts, later you said in the middle of the movie), or what app/service you are using - Is this the Disney+ app/service, or the Disney channel within a TV provider's app (e.g. Spectrum TV, xFinity, YouTube TV, Hulu TV, etc)
Its also not clear when the "flash black" occurs with other apps - does this happen when loading the app, or when the app is already loaded and content is selected to play?
If the latter, this is sometimes due to an HDMI refresh rate sync issue - try manually configuring your Display type: Settings/Display type = 1080p TV/4K TV/4K HDR TV/etc (do NOT use Auto) and disabling framerate matching: Settings/System/Advanced system settings/Advanced display settings/Auto-adjust display refresh rate = off