Comment 3 for bug 1724561

I suspect the issue is that you are using MySQL as the database manager and because of https://gitlab.com/mailman/mailman/issues/385 you have a truncated entry in the 'pending' data. Deleting the list is trying to remove the pending requests for the list and the truncated data is broken in the middle of a '\u' sequence. This throws the exception.

You will probably have to manually remove the offending entry from the pendedkeyvalue table.