Are you using the NowTV App with a Mobile IOS or Android device ?
What TV show or Movie are you trying to download where not all movies or TV shows are downloadable due to Rights Restrictions.
See if this linked article helps in anyway.
If you can post a name of the TV show or Movie (Disney films are not downloadable from what i can see) that you are looking at, i will double check on my Android Tablet when using the NowTV App if i can see the Download Arrows on my device.
Yeah perhaps delete the NowTV App from your Android Samsung Mobile and download the NowTV App again from the Google Play Store.
I have just checked The Young Pope on my Android Tablet and next to each episode it shows the Download Arrow.