An additional force is applied when you select unsymmetric faces or edges about the specified bearing force direction. A message alerts you when the additional forced is more than 5% of the applied bearing force.
In the example below, the selected entity is not symmetric about the specified bearing load direction. The horizontal components of the transferred load P along the circumference clearly do not sum to zero.

The additional unbalanced load is calculated by the following equation:

U.F. denotes the unbalanced force.
For sinusoidal load distribution:
Px = P cosΘ = Fo sinΘ cosΘ
For parabolic load distribution:
Px = P cosΘ = Fo sin2Θ cosΘ
The percentage of unbalanced load is calculated as (U.F./F) x 100.
In general, the mesh refinement and the location of the node affect the calculation of the unbalanced force due to the variation of Px along the circumference.