Pymeshlab claiming files are not present when they are?

Question

I have two pymeshlab scripts:

import os
import argparse
import pymeshlab
from collections import Counter

def load_mesh(file_path):
    ms = pymeshlab.MeshSet()
    ms.load_new_mesh(file_path)    
    measures = ms.get_topological_measures()
    print(measures)


def main():
    # Parse command-line arguments
    parser = argparse.ArgumentParser(description="Count the number of 'ok' meshes in a directory.")
    parser.add_argument("-i", "--input", required=True, help="Path to the directory containing OBJ files.")
    args = parser.parse_args()

    results = load_mesh(args.input)


if __name__ == "__main__":
    main()

And

import os
import argparse
import pymeshlab
from collections import Counter

def is_mesh_ok(file_path):
    try:
        ms = pymeshlab.MeshSet()
        ms.load_new_mesh(file_path)
        measures = ms.get_topological_measures()
    except Exception as e:
        print(f"Failed to load mesh '{file_path}': {e}")
        return "Load Failed"

    genus = measures['genus']
    connected_components = measures['connected_components_number']
    is_two_manifold = measures['is_mesh_two_manifold']
    hole_count = measures['number_holes']

    is_ok = (genus == 0) and (connected_components == 1) and (is_two_manifold is True) and (hole_count == 0)

    if is_ok:
        return "OK"
    else:
        failed_criteria = []
        if genus != 0:
            failed_criteria.append("Genus")
        if connected_components != 1:
            failed_criteria.append("Connected Components")
        if not is_two_manifold:
            failed_criteria.append("Is Two Manifold")
        if hole_count != 0:
            failed_criteria.append("Number of Holes")
        return ", ".join(failed_criteria)

def count_ok_meshes(directory_path):
    results = []

    for filename in os.listdir(directory_path):
        if filename.endswith('.obj'):
            file_path = os.path.join(directory_path, filename)
            result = is_mesh_ok(file_path)
            results.append(result)

    return results

def main():
    # Parse command-line arguments
    parser = argparse.ArgumentParser(description="Count the number of 'ok' meshes in a directory.")
    parser.add_argument("-d", "--directory", required=True, help="Path to the directory containing OBJ files.")
    args = parser.parse_args()

    results = count_ok_meshes(args.directory)

    counter = Counter(results)
    
    print("Histogram of Failed Criteria:")
    for key, value in counter.items():
        print(f"{key}: {value}")

if __name__ == "__main__":
    main()

I am calling both on the same files, they are on the same directory. The short script seems to work, but the large one claims it cannot find some of the files, I don;t understand how. For example the large one shows this error:

Failed to load mesh 'clean_results/mesh703.obj': File does not exists: clean_results/mesh703.obj

For the exact same file the small one returns:

{'boundary_edges': 0, 'connected_components_number': 1, 'edges_number': 4629, 'faces_number': 3086, 'genus': 0, 'incident_faces_on_non_two_manifold_edges': 0, 'incident_faces_on_non_two_manifold_vertices': 0, 'is_mesh_two_manifold': True, 'non_two_manifold_edges': 0, 'non_two_manifold_vertices': 0, 'number_holes': 0, 'unreferenced_vertices': 0, 'vertices_number': 1545}

It also only happens with some files, not all, and seems to change between invocations. I don't understand how this is happening. Why is the large script failing to find files using the exact same logic the small one is using?