Hi,
I would recommend updating your HikaShop as we've done some patches on the payment notifications since the 3.5.0
So it could be linked to that.
The screenshot indicates that the order id is not provided.
Do you get normal payment notification emails for the orders ? Are they confirmed automatically by the PayPal plugin ?
Normally, no email should be sent if the order id is missing from the notification or is invalid (which could happen if someone was trying to send fake payment notifications to you).