I've got the same problem as rpain on 7th december where the transaction is successful and return to the site has blank order number.

The 'epdq_log' table shows that the transaction was successful but the order doesn't appear in my 'orders' table and so isn't shown in orders on my ZenCart admin page.

Trying the simulated ending by calling epdq_cpi_handler.php just does the same thing and returns to the 'Thank You' page with a blank order number and nothing added to the 'orders' table.

The shopping cart still contains the products ordered and so isn't cleared.