Most of the time, the Poloniex API import works properly.
If you are facing problems, please set up the Poloniex API again, with a new key and see if this fixes the problem.
It seems like Poloniex sent wrong values a few months ago, their support confirmed that.
Make sure it didn´t affect your account and if necessary,
compare the entries on the Transactions page with your data on the Poloniex "History" page.
If there is something missing, enter the data either manually or via one of our "Bulk Imports".
Another solution would be, to first use the Poloniex CSV import for the initial setup and after that,
to activate the API job with a starting date of today. This way, only future transactions will be imported.
Unfortunately the Poloniex CSV and API import are not compatible.
If the CSV import was used, we also display this on the API import page.
I recommend you delete all Poloniex data and import everything via CSV, as before.
Afterwards, you set a start date for the API job, so that only future transactions will be imported.
Usually our system compares transactions via the trade ID.
This is not possible for the Poloniex API export.