I can't see why this error is being produced. the grouping step has all the data required to create the output.
Are you grouping results of a Validate address step? If so we have seen this case previously and will work to resolve the issue.
If not would you be able to share an export https://docs.experianaperture.io/data-quality/aperture-data-studio-v2/monitor-data-and-troubleshoot/migrate-metadata/#exportfromaspace please so that we can investigate further.