What app is this happening with? You only mentioned that it doesn't occur with any other one. Or is All 4 the name of the channel? I don't recognize the name. Are you located in the US, or somewhere else?
Since it's only happening on a single channel, I would concur that there's likely no networking issue causing it. It's possible the provider themselves are having difficulty with their streaming servers. The other possibility is there's an issue with the channel itself, and only the channel provider can resolve that. Roku did not create the channel and can't make changes to it.
When you remove a channel, you must reboot the device before adding it back. For a Roku TV, that doesn't mean turning it off and on, as that doesn't really shut the TV down. Go into the Settings/System menu and find the System Restart setting and reboot it that way.
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