You have exported a report from DLP into .csv format
When the report (.csv file) is opened in Excel, the dates are not recognized as a date/time type and cannot be correctly sorted.
The DLP Enforce server uses the US-English short date format when exporting data to CSV. Due to other internal dependencies, this is not due to be changed.
Change the locale in the Region control panel on the Windows workstation machine to English (United States) before importing the CSV file:
In newer versions of Excel you can designate the region of the imported source CSV file: