Viewshed not always producing a visible range

[SchuylerBorges]

Hello! So I am trying to create a viewshed for 25 different points. However, the viewsheds work for certain observer points and then not for others. Out of the 25 different observer points I have, 7 do not have a "visible" field. I am just wondering why this is. All of the points should be able to see something. An example of what happens when I try to do a viewshed for one point is below. It is the attribute table for that point.