Hello - we are seeing seemingly random drops in responses from Auth.net. With the debug log on, we saw a customer place 2 orders, the first has no response, and the 2nd, placed half an hour later, went through fine. There is no record of Auth.net ever receiving the first request, and the customers order is still in 'Pending' state (rather than 'Processing,' which occurs after the payment has been confirmed).

The 2nd order was placed, there is a record of the transaction in Auth.net and the customers order has been processed in Magento as expected. 

How can I determine why the initial order did not receive a response? From the payment log:

[2018-08-31 16:53:04] main.DEBUG: array (
  'request' => 
  array (
    [order data] // FIRST ORDER, NO RESPONSE
  ),
) [] []
[2018-08-31 17:17:51] main.DEBUG: array (
  'request' => 
  array (
    [order data] // SECOND ORDER, SUCCESSFUL RESPONSE
  ),
) [] []
[2018-08-31 17:17:54] main.DEBUG: array (
  'response' => 
  array (
    'x_response_code' => '1',
    'x_response_reason_code' => '1',
    'x_response_reason_text' => 'This transaction has been approved.',
    ...
  ),
) [] []