Bug at mixing matrices computation (return empty dictionary)

[gcanasherrera]

I'm encountering an unusual issue with heracles when computing mixing matrices, using the current example notebook provided.

On the first run, the heracles.mixing_matrices() method works as expected and successfully produces the mixing matrices.

However, on subsequent runs of the notebook — even after restarting the kernel — the same method consistently returns an empty dictionary. This happens despite the input dictionaries (fields and cls) appearing correct, with all expected keys and arrays present.

Environment

• heracles installed from the main branch via pip
• Python: 3.10.16 (main, Dec 11 2024, 10:22:29) [Clang 14.0.6]
• Platform: macOS-15.4-arm64-arm-64bit
• Architecture: 64-bit

Troubleshooting Attempts

• Restarted the Jupyter kernel
• Cleared .ipynb_checkpoints and related Jupyter cache
• Reinstalled heracles

Any insights into what might be causing this inconsistent behavior would be greatly appreciated.