Sen2Cor provides Bottom-of-Atmosphere (BOA) reflectance (level 2A product). To obtain water-leaving reflectance (Rhow) or remote sensing reflectance (Rrs), you’ll need to perform atmospheric correction and additional processing steps, using specific algorithms and data relevant to your study area.
you can check https://step.esa.int/thirdparties/sen2cor/2.10.0/docs/S2-PDGS-MPC-L2A-ATBD-V2.10.0.pdf
You can also find this 'NoneType' object has no attribute 'box_id' - #8 by Sen2cor_dev_team usefull.