I have tested and got the issue and already reported to the developer team. I will try my best to get this solved ASAP.

Hello All,

I have tested this issue and found a temporary fix. Open “wp-content/plugins/dokan-seller-vacation/dokan-seller-vacation.php” and go to line number 150

You will see their a comment “All Scripts Go Here”, then paste the following code on the next line
wp_enqueue_script( ‘jquery-ui-datepicker’ );

This should fix the issue. Please check and let me know.

I have it working. But I think it is a provisional solution.
When you refresh the page, you can still see that it is happening and after a little time it makes the correction.
You cant test it on http://www.authorproducts.com
Thank you!