What happens is that some videos can not be downloaded.
To explain a little bit better, let's use the image below which shows the download and play buttons with different colors:
(Although iPhone or iPad appear below each button, these colors are the same on Android devices)
- When videos can be downloaded, image 1 will appear.
- When the videos have been downloaded and saved, the "Play" button has the fuchsia / pink color as picture number 2.
- The gray "Play" button appears when the video is streaming and there is no Internet connection to watch them at the moment, as in picture 3.
- If the "Play" button is yellow, the videos are streaming and the internet is available to watch them at the moment.
In other words, the streaming videos you can watch the video, but do not download it and save it into your device.