@sbasiima, just checked your setup.
So your original question,
With the new workflow you can flick between the boundary condition definitions to see what is highlighted:
Here we can see that you have selected the bounding box as well as the drone for the ‘drone’ boundaries.
Slip walls have been selected for the symmetry.
and flicking between symmetry and slip walls you have missed the x high wall from either.
my general workflow here is as follows:
Assign the inlet and outlet boundaries then hide them
Assign the slip walls then hide them
Assign the symmetry faces then hide them
Assign the MRF then hide it
‘select all’ the assign to the drone
By the end, if you have done all the boundaries nothing will be visible!!