If you're using any kind of ad or content blocker, disable it. Then try a "System restart" from Settings->System. If that doesn't help, try a "Network connection reset" from Settings->System->Advanced system settings. You'll have to reconnect to your network afterwards. If still no luck, restart everything involved - gateway/modem/router and Roku device. Finally, try connecting to an alternate network like your phone's hotspot if possible. If it works when connected to an alternate network, then there must be something about your network that's causing the problem.
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