What you show in the video is by design; once an email-address that has been used to place an order is entered, the system will remember this (using a session variable).
So now we have to find out why new customers sometimes don’t get the free item. Please send to admin at soft79.nl:
– the coupon settings (temporarily enable Settings > WC Extended Coupon Feature > Debug mode and click on ‘Coupon data’-link on the Miscellaneous-tab of the coupon.
– an order confirmation of an order that didn’t receive the free gift, but should have received the gift.