Cookie missing after redirecting from payment site

[Richard Plangger]

Hi,

I have implemented another payment provider which is rather omnipresent in the European regions (e.g. Austria, Germany, ...). It is called Sofort.com.
I'm fighting an issue I cannot reproduce locally and maybe somebody has an idea how to solve this issue:

In production after the payment has been processed on sofort.com the customer's browser is redirected to the following URL:

<mysite.com>/sofort/success/<transaction-ID>

But on this request in production there is no cookie data. Which means that neither a name, address can be matched the payed basket and the order cannot be created.
What causes this behavior?

Cheers,
Richard