Missing pathways

I used the function humann2_regroup_table to identify reactions in my dataset, and some of the identified reactions don’t belong to any of the pathways listed in the file “pathabundance.tsv”.
From what I understand, minpath should find the minimum set of pathways to explain all the reactions that are liked to pathways. However, many reactions belong to multiple pathways, and any of these pathways are listed in the file “pathabundance.tsv”. Could you help me to understand why is this happening?
Thank you.