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.
Workstation with a non-US English region locale applied.
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: