Add comment about issue 42676

app/models/diff_note.rb

@@ -134,6 +134,7 @@ class DiffNote < Note
       # `Diff::FileCollection::MergeRequestDiff`.
       file = noteable.diffs(original_position.diff_options).diff_files.first
       # if line is not found in persisted diffs, fallback and retrieve file from repository using gitaly
+      # This is required because of https://gitlab.com/gitlab-org/gitlab/issues/42676
       file = nil if file&.line_for_position(original_position).nil? && importing?
     end