Problem with PayPal IPN after upgrade

I upgraded from 1.3.7.1 to 1.3.8, then removed and uninstalled PayPal IPN with the same settings.

Now when an order is placed, the funds are withdrawn from customer's PayPal account, but customer is not receiving order confirmation email. Nor is the order being listed under "New Orders".

Orders using "COD" works fine.

How should I proceed to fix?

When I view ipn_main_handler.php via the browser, I'm getting a white blank page.

Blank white pages are indicative of PHP errors introduced by code alterations.

Using debug logging tools will usually provide assistance in diagnosing the problems you're encountering. FAQ on blank page situations: https://www.zen-cart.com/tutorials/index.php?article=82

Thanks for the tips.

And after much experimentation and debugging, I have confirmed that my problem stems from bad interaction between the "Simple SEO URL" module and PayPal IPN. See thread here.

Not just me, see thread here and here.