The Coinbase API Import is provided as a BETA version. It may not work with all accounts correctly.
Output formats sometimes change from user to user.
In most cases it is necessary to go through your data from the Coinbase website and to correct it manually or with one of our "Bulk imports".
(For example the "Excel Import")
At least, after that´s done, it becomes pretty stable for new transactions to automatically be imported by the Coinbase API import. (Beta)
(Keep in mind to first do an initial upload with the API import and then to correct the data. In this case you should not use another importer because they are not compatible.)