If you ever get below error  :
DateTime::__construct(): Failed to parse time string (11/08/2019) at position 0 (2): Unexpected char

Here is the solution

Update this file : /vendor/magento/module-catalog/Controller/Adminhtml/Product/Initialization/Helper.php

Add one line code :

private function convertSpecialFromDateStringToObject($productData)
{
    if (isset($productData['special_from_date']) && $productData['special_from_date'] != '')
    {
        $productData['special_from_date'] = $this->dateFilter->filter($productData['special_from_date']); /* Add this line */
    	$productData['special_from_date'] = new DateTime($productData['special_from_date']);
    }
    ...

Hope my post is helpful. If you are facing problem during this process, then feel free to comment.