I tried many ways to make it work. Mailchimp allows date format in dd/mm/yyyy or mm/dd/yyyy. But elementor provides in yyyy/mm/dd. I also tried to change the date format of elementor form following this link.
The trick that worked here is I switched the date field in elementor to HTML5 date. This way, we are not loading the third party date plugin – FlatPikr & using the native HTML date plugin.
So, this worked perfectly.
Let me know if this helped anyone out there as it really took me some time to troubleshoot this issue.