Thank you so much for your reply, Rob.
You are absolutely right. After disabling the accuracy control, the total number of tracking steps for a single parcel was increased from about 2300 to about 40000 (still, the path is updated only once in some of the cells which I am not sure why? Maybe the parcel passes through a very small part of those cells and doesn't traverse through the whole cell, i.e. doesn't go from one end to another end of the cell)
These are 3 different zooms of my mesh. The height of the first layer of mesh, right above the walls, is about 3e-7m according to the third photo in the following.
At high velocities (above 1m/s) because of the higher inertia of the particles, they cannot follow the sudden change of streamlines close to the wires well enough and hit the walls and get captured (filtration by impaction mechanism). My wire diameter is 0.05mm (50 microns) and the wire distance (i.e. aperture size) is 0.1mm (100 microns). the porosity of the screen (ratio of the area covered by the wires to the total area) is about 60%.
I currently observe about 60% removal of the 1-micron particles at 1m/s.