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Does the issue only occur on the NBC channel or across other channels installed on your Roku device?
Have you tried removing the affected channel NBC channel and then re-install again? If not, we suggest starting there. In some cases, removing the affected channel and then re-installing it may help. Restart your device before re-adding the channel back in to ensure the process is successful. We recommend doing this through the Settings menu by navigating to Settings > System > Power (If there is no Power submenu, proceed to the next step.) > System restart.
For detailed instructions, refer to this Support link for more information: How to resolve a channel playback issue | Official Roku Support.
Let us know if there's any difference after.