Pathologic was missing because of a .git folder inside.

[yaffs-website] / web / modules / contrib / slick / slick_ui / slick_ui.links.menu.yml

entity.slick.collection:
  title: Slick
  route_name: entity.slick.collection
  description: 'Manage Slick optionset.'
  parent: system.admin_config_media

slick.settings:
  title: Slick UI
  route_name: slick.settings
  description: 'Manage Slick UI.'
  parent: entity.slick.collection
  weight: 21