The history of imports made by users can be found after going to the data import module, available in 3 places in the system described here.
Below the list of data import options there is a table with a list of all imports (both successful and unsuccessful attempts):
The table contains the following information:
Import author - name and surname of the user who made the import
Date - day and time the import was made
File name - the name of the .csv file from which data was imported
Import type - information whether it was import of new or update of existing candidates
Import status - information on whether the import was successful or unsuccessful
Error report - the column in which the file with the error report is located and can be downloaded. The error report contains a list of records for which the import failed - along with the reason for the failure.