An upgrade or two back our Rails 6 app lost line comments. I can’t remember if it was trying to improve speed or the upgrade to sassc. Well it’s fixed now.

# Debug mode disables concatenation and preprocessing of assets.
  # This option may cause significant delays in view rendering with a large
  # number of complex assets.
  # config.assets.debug = true
  # config.sass.line_comments = false
  config.sass.inline_source_maps = true

Thanks https://github.com/sass/sassc-rails