Alright, if you open the script in a text editor you can clearly see the lattice vectors are not completely perpendicular:
vector_a = [15.0, -0.00900547, 0.00431798]*Angstrom
vector_b = [-0.0186507, 25.0, -0.0119156]*Angstrom
vector_c = [0.0222371, -0.0296296, 65.0]*Angstrom
I don't know how you generated the structure, but if you built it from a structure obtained after a relaxation or from someone else, or made "by hand", it is easy to introduce tiny numerical errors. You can either start from a "pure" structure that is mathematically defined or use the lattice/unit cell tools in the builder to ensure that the lattice vectors are exactly perpendicular.
For now we can fix this by changing the lattice vectors in the script to:
vector_a = [15.0, 0.0, 0.0]*Angstrom
vector_b = [0.0, 25.0, 0.0]*Angstrom
vector_c = [0.0, 0.0, 65.0]*Angstrom