Can one or both of you do the following for me. Add this line to your wp-config.php:
define(‘PMPRO_IPN_DEBUG’, true);
Then test a checkout to completion. You should get an email to the WP admin about the IPN. It might have an error in it. Paste that error (or non error) here so I can take a look. Thanks.
If there are emails or other info in the message, you can scrub them but make sure I can tell that they are different. One common issue is when PayPal is using a different email from your standard PayPal email to create IPN requests. These can get rejected by PMPro, but there are ways to tell PMPro to account for the new email. Might be something else, but might be related to this.