It’s possible that the sort function is having difficulty with this particular date format. In that case, there’s a way to pass a timestamp for each column’s value for sorting purpose.
The Col
tag accepts an optional attribute value
, which is used for sorting, separate from the displayed value (the formatted date).
<RowLoop type=voca>
<Col value="{Field publish_date date_format=timestamp}">
<Date><Field publish_date /></Date>
</Col>
</RowLoop>