Thanks for letting us know about the issue you're experiencing.
If you haven't tried yet, you can remove NFL then re-install it. To ensure the process is successful, make sure to restart your device before adding the channel back in. We would recommend doing this from the Settings menu by navigating to Settings > System > System restart > Restart.
For detailed instructions, refer to this Support link: How do I resolve channel playback issues?
Let us know if this works for you!
All the best,
Roku Forum Moderator