No physical meaning in results (DAGMC, Unstructured Mesh)

Hi!
I’m simulating a nuclear spent fuel element transport container, performing the simulation directly on the CAD model through DAGMC. Also, i’m using an unstructured mesh tally to visualize the photon flux in the air around the container. After running the simulation the results I obtained don’t make sense to me so I’m writing to see if you can see any mistake that I’m overlooking.
In the first pic you can see a plot of the geometry, a MTR fuel element surrounded by lead (blue). Air is light blue. The simulation has multiple sources (meat in each fuel plate), and the results are in the second pic (using write_data_to_vtk function). As you can see in one side of the geometry there are no photons at all and that is disturbing me. Shouldn’t it be symmetrical?
Any ideas of what could be happening? Thanks in advance!