Importing uid of the author into article nodes fails 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
The difference is that the fid you're migrating is part of a reference field with an internal structure, which makes 'iterator' appropriate. For nodes, however, uid is a simple property, not a field array, so you can map it more directly:

process:
  uid:
    plugin: migration
    migration: luxus_users
    source: uid