CSV import generates duplicate options for "Select List" custom fields

Summary

Upon performing CSV import, Multiple duplicate options/Values are being generated for  the "Select List" custom field though the value defined in csv is the same as the existing values.

Diagnosis

Export one existing record from a site that includes the value in question on the issue. Compare the value you have and the exported file whether the value has space or a different special character.

Cause

The value for the said field may have space or format change or a different special sign (like hyphen etc) in the CSV file ; therefore, duplicate values get created for the fields.

Solution

It is recommended that you copy the desired value from the exported file and update it for all records in the CSV file(Required to import). This should mitigate the problem.