Welcome to the forum. It could be something as simple as the wireless channel your router is set to has too much interference, try rebooting the router to force it to choose the best wifi channel, and also make sure both it and the NOW TV box are in an open, clear space as much as possible (not on crowded shelves, inside cabinets,men T to sources of interference etc).
However I'd recommend giving the broadband team a call, they can test the line and router and also offer further advice. Calls are free.
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