Even though a field map is configured in the transform map and the correct data is imported, the transform map fails to update the field on the target table.

This scheduled import has the 'Run as' user as one with no roles. 

For an import to successfully run and transform the data, you should give the role 'import_admin' to the 'Run as' user configured in the scheduled import. 
This role contains the roles import_set_loader, import_transformer and import_scheduler roles and without these roles, the import will not work as expected.