Loss of contact between pantograph and contact wire is: 

In an overhead railway system, the pantograph (the device that collects electricity from the contact wire) can lose contact with the contact wire due to several factors, such as vibrations, irregularities in the wire, and changes in the tension of the wire.

At the support (near the poles/towers), the tension in the contact wire is generally higher because it is fixed at the supports. The wire tends to sag more in between supports, leading to potential fluctuations in the distance between the pantograph and the contact wire. The pantograph is more likely to lose contact at the support where there are more dynamic forces acting on the wire.

At mid-span (the point between supports), the tension in the contact wire is usually more uniform, and the distance between the pantograph and the contact wire is less likely to vary as much compared to the support points.

Thus, the loss of contact is typically more at the support than at mid-span.​