My custom Drupal 7 to Drupal 8 migration correctly follows dependencies and first migrates users, then articles. The problem is that it fails to import user IDs into the 'uid' field and leaves it at '0'. For uid processing, I use the following YAML snipped. Note that 'luxus_users' is the user migration that works fine.
process:
uid:
plugin: iterator
source: uid
process:
target_id:
plugin: migration
migration: luxus_users
source: uid
I hoped would work for me as similar one for file migration already works for me.
field_logo:
plugin: iterator
source: field_logo
process:
target_id:
plugin: migration
migration: luxus_files
source: fid