Hi,
Because you see a message in the log file (which is a warning fixed in HikaShop 2.2.2) it means that Paypal call your website.
The warning is not a real problem because it does not stop the process of the order modification.
If you see the warning in the log file, it means that the process worked that's why HikaShop write the content in the log file, otherwise the process should be stopped and the log file will stay empty.
My "problem" is that, the IPN return is made by the plugin before the process of the message. It means that the IPN validation works if you have "confirmed" in one side and "sent" on the other hand.
But for me, the warning message is not a sign of real problem because if you see it, it means that the order has been modified (so I guess, confirmed).
Edit
Some ideas:
* Test the IPN url directly in a browser (with cookie cleaned) in order to see if there is any kind of redirection. - Looks good
I will continue to make some tests and investigate.
The fact is, if the process suddenly "work" it make the feeling that it could be something link with the firewall, a wrong notify url (if you access the website using a url which does not really exists, the plugin will use this url for asking the IPN callback), or a list of IPN in the plugin (but you will receive an email to notify you).
Regards,