Answered Save() fails on some records and not others

I'm using the cmpGenerator package to interface xPDO with an external database as I have done many times before. The snippet is iterating over around 400 records in an array produced from a vendor restful json api and inserting or updating them if necessary one at a time.

The problem is some rows are inserting while others are failing to save. No errors are returned on screen or in the error logs and I cannot see anything funny about the data that would cause problems. All fields are varchar(255) or int(11), NULL default, and the table has an auto_increment primary key index. Pretty standard. Anybody have any thoughts why this is happening? I've tried several methods to get an error message out of xPDO but everything returns an empty array or empty message.