How can I import fields into Drupal 8.4 user profile from a csv file that has identical values in the key row? I'm using Migrate Tools, Migrate Plus and Migrate Source CSV. My CSV file looks like that:

"Stg";"Color";"Fruit"
"user1";"red";"apple"
"user1";"blue";"pear"
"user2";"green";"banana"
"user2";"black";"rotten banana"


I'm using the Profile Module (https://www.drupal.org/project/profile)

I have a migration within my migration group that looks like this (migrate_plus.migration.user_vorlesungen.yml):

id: user_vorlesungen
langcode: de
status: true
dependencies:
    enforced:
        module:
            - user_migrate
migration_group: hoevwa
label: 'HoeVWA Vorlesungen Import'
source:
    plugin: csv
    track_changes: true
    path: /config/Vorlesungsverzeichnis.csv
    # Column delimiter. Comma (,) by default.
    delimiter: ';'
    # Field enclosure. Double quotation marks (") by default.
    enclosure: '"'
    header_row_count: 1
    keys:
        - Stg
destination:
    plugin: entity:profile
process:
    type:
        plugin: default_value
        default_value: 'vorlesungen'
    uid:
        plugin: migration_lookup
        no_stub: true
        # previous user migration
        migration: user__hoerer
        # property in the source data
        source: Stg
    # These field have multiple values in D8
    field_color: Color
    field_fruit: Fruit

migration_dependencies:
    required: {  }
    optional: {  }


In my YAML file the content is printed like that:

...
&lt;table&gt;
  &lt;tr&gt;
    &lt;td&gt;{{ content.field_color }}&lt;/td&gt;
    &lt;td&gt;{{ content.field_fruit }}&lt;/td&gt;
  &lt;/tr&gt;
&lt;/table&gt;
...


When I run drush mim --group=hoevwa only the last values of user1 (blue, pear) are imported. How can I get running a process plugin to loop through the CSV and get all values imported. And finally how can I loop through all values in my TWIG Template?
The solution will be to create a custom Migration Source Plugin and do some magic in the fetchNextRow() method. Depending on the source of your data, you might also use some other approach.