I tried a text CSV file with three lines:
First Name,Last Name,Primary Email,Display Name,Job Title,Groups
Test1FN,Test1LN,test1@example.com,Test1 DN,Test1 Title,PTG3 Publicity
Test2FN,Test2LN,test2@example.com,Test2 DN,Test2 Title,PTG3 Publicity
and the two contacts were imported. The first five fields were imported properly, but the two contacts were not added to the desired group (nor to any group). What am I doing incorrectly? Thanks.