Seems like the inventory_parts.csv file from https://rebrickable.com/downloads/ is incomplete. For example, there is nothing with inventory_id 23385:
while in inventory_sets.csv, there is:
However, the information is present in the database as shown by:
curl -X GET --header 'Accept: application/json' --header 'Authorization: key XXXXXXXX' 'https://rebrickable.com/api/v3/lego/sets/10706-1/parts/'