I am importing data from Trac into JIRA cloud. I have couple of custom fields in the import - Customer and Trac URL.
I have created a custom fields on the the Project Settings > Issue Types > Create new Field.
Then I tried import and while the import presented the fields at time of import and allowed me to map the field to a field present in the source csv, post import I did not see any value against the imported field.
JIRA in built fields had proper values.
I also tried creating Custom Field using
Jira Settings > Issues > Custom Fields
Then I did the CSV import. Again the import presented my newly created custom field while importing but the values do not show up after import.