A suggestion is to ensure software and app is fully updated.
Another suggestion is to set the box to factory settings as this often squashes bugs on the system.
Then worst case to report the fault directly with Now TV by either Live chat
Just make sure to click “chat online” within the green box
Or send an email to the address found in the picture below
This is most likely an issue with the channel itself, or your local Freeview Transmitter. I’d suggest contacting London Live so they can look into it, unfortunately it’s nothing to do with Now TV.