I’m not sure what goes wrong. Either Sen2Three writes the product wrong or S2TBX is reading it wrong.
I assume that you have the latest S2TBX updates installed.
I have analyzed the files and it seems that some metadata items have changed in the version 1.0.1. I have modified the L3 reader to be able to manage this, it should be fixed with the coming module update.
Meanwhile, it should work properly if you modify manually the granule metadata file in line 9530: replace the PVI filename “S2A_USER_PVI_L03_TL_MTI__20150812T154929_A000534_T32UMA” by “S2A_USER_PVI_L03_TL_MTI__20150812T154929_A000534_T32UMA_8”