Earlier I was facing
PayPal IPN postback failure issue in my Magento store version 22.214.171.124 I am using
Paypal Website Payment standard method.
I have fixed this issue using link http://www.dhmedia.com.au/article/debugging-paypal-ipn-postback-failures-magento
Now from few days back I started getting same issue again for some paypal orders and it is quite random, for some users it is coming and for others it is working fine.
Also we are using SSL on our store.
What can be the probable issues and how can I track this?