To resolve, the Employee value on the CSV Import file should either contain:
1.Employee Internal ID - As best practice, using this is highly recommended avoiding any related errors with the incorrect Employee Name.
2. Employee Name – Should contain the exact format as seen on the User Interface (via Global Search or in the Time Tracking Form's Employee field).
*Note: Depending on which was entered in the CSV Import file, in the field-mapping page, click on the small pencil icon beside the Employee field and Choose Reference Type to either Internal ID or Names.