The issue was a rubocop control comment recently added in test/factories.rb:

FactoryBot.define do # rubocop:disable Metrics/BlockLength

Removing the comment lets the generator match FactoryBot.define correctly again. Wrapping the define statement in rubocop control comments on different lines works as a short term solution until we split our many factories out into different files:

# rubocop:disable Metrics/BlockLength
FactoryBot.define do
  # rubocop:enable Metrics/BlockLength