I can’t find anything specific on the Crossref domain that explains this error, but I get the impression that this error is just letting us know that this DOI was resubmitted. Can you provide some insight into what the duplicate key was? I assume that we are submitting XML multiple times and this error is letting us know that.
Thanks for flagging that error to us. We thought we fixed this last month. I have simply rerun submission 1661159289 and that cleared things up. I have flagged this error back to our technical team so they can investigate the underlying cause. If you see this error again, please do let me know.