Problem importing CSV/vCARD contacts to S3
The reason I had this issue was a badly formatted vcard file. There were many BEGIN:VCARD tags that were not closed with END:CARD tags. As an example, it looked like this:

BEGIN:VCARD
VERSION:3.0
BEGIN:VCARD
# Bunch of fields in here like N, FN, EMAIL, etc.
END:VCARD


As you can see, the first BEGIN:VCARD is not closed.

So in a text editor, I did a Find and Replace to get rid of any unclosed BEGIN:VCARD, such that it looked like:

BEGIN:VCARD
VERSION:3.0
# Bunch of fields in here like N, FN, EMAIL, etc.
END:VCARD


After doing that, the vcf file imported without any problems.