I have an excel sheet with a table containing two Date formatted columns.

In my flow, I am using the List Rows from Excel connector, with the ISO 8601 date format configured:

This is a twice daily scheduled flow and was previously working as expected, until the behaviour changed early on November 30th. without the flow being modified:

Since this run, my first column is coming back as a correctly formatted ISO 8601 date, but the second column is coming back as the Excel serial date format:

In Excel, neither column has been updated and are both still Date formatted, and in Flow the connector is still configured to use the ISO 8601 formatting.
I would wonder if it was a limitation of the connector for only the first Date column to obey the formatting configuration, but it was working for weeks after I initially created the flow.