I'm trying to migrate a multi-value D6 image field to D8. I've already migrated the files with d6_file and it worked. When I do the node migration with the image field works and I get all the values but the alt and title text are not migrated.
field_image:
plugin: sub_process
source: field_image
process:
target_id:
plugin: migration_lookup
migration: upgrade_d6_file
source: fid
alt: alt
title: title