Hi,
When you pay an order with points, the order is directly created with the status confirmed.
So the order creation email is sent to the user, but the order status notification (which is sent to the user when a payment plugin changes the status of an order from created to confirmed) is not sent since the status is not changing.
I suppose you must have disabled the order creation notification email so that people paying with Mollie only receive the second email, which leaves the users paying with points without any email.
Normally, in such case, the total amount of the order should be zero, so you can enable the "Hikashop Validate free order Plugin" via the joomla plugins manager and make sure its "Send confirmation email" setting is on so that the customer will receive the order status notification.