When you are using the Player Insights page to gain an understanding of how your viewers are engaging with your video, the attention span data (also known as Combined Viewers) will appear under certain conditions.
You notice that the Attention Span is either not showing on the Insight page, or in the export like below.
The reason for this is due to the data that is currently being filtered, containing more than one video.
It does not make sense to display an attention span graph of multiple videos, as the data is not useful.
You may have tried to filter on an individual player but this player could contain more than one video, so results in this issue as well.
You will need to use the Videos filter and select only one video from the list that you see.
If the player only has one video, the graphs and extract will work without the need for additional filtering.