This may have something to do with the archive database. You can try the script at https://www.msapiro.net/scripts/hddump to dump the database for the affected period with --verbose and look for values of 'author' and 'decoded'['author']. Is there anything unusual in those or anything with a number like 'Doe, John 3rd'.
If you can post one of the shunted message files or email it to firstname.lastname@example.org if you don't want to post it, I'll see if I can duplicate this, but also, please see https://wiki.list.org/x/12812344 .
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** Changed in: mailman Assignee: (unassigned) => Mark Sapiro (msapiro)