Hi Elizabeth,
I opened your CSV in LibreOffice Calc (which I often recommend over Excel for preparing CSV files, since it allows you to set the encoding and separators before opening a CSV file, while Excel often defaults to its own custom character encoding such as WinLatin), and the dates looked okay to me.
I removed the qubitParentSlug value (since I don't have your parent record), and added a legacyID value, then imported it into my local 2.4.x test environment. I'll attach the CSV here for reference.
The dates seem to have imported fine for me:
Quick question: were you looking for your start/end dates in the display page, or did you enter edit mode to check the controlled fields?
The start and end dates are typically not shown to end users in the view pages - the display date is instead a free-text field that allows for approximation and uncertainty to be expressed with text and special characters, as per local conventions.
It is possible there is some bug we didn't know about in the 2.4.0 release, but if so, it appears to be resolved in the upcoming 2.4.1 release. We're in the final stretch of release testing now, and hope to have a public 2.4.1 release available very soon!
Regards,