Cyclic condition implementation for particle flow in computational domain

Its Mfix DEM simulation of gravity driven particle flow.
In the above image, the cyclic BC condition is applied along Y-axis.
Also gravity is applied in the Y- direction.
The particle flow is looping but some particles are seen coming out from the domain. It shouldn’t happen. The particles should only flow inside the computational domain.

How should I rectify?

Did you define a wall BC for the half-cylinder?