This could be due to a mismatch of the subscriber ID for whatever reason. Then if the notification comes with an ID that s2Member doesn't find in the DB, it goes nowhere.
Payment notifications go to the accountant. They are no use to me - I need the data in the database!
Of course. I didn't mean the PayPal notification by email, I meant the s2Member Notificatoins API, which you can then use to populate your database using a simple script. See the article I linked to above about a notification handler.
is there a way to repopulate/sync this from paypal?
Not yet, but this is something I'll look into when I build the new logging routines. I'll also want to find a way to get in data that goes back to populate the database. I still don't know how far back I can get from PayPal, haven't studied it yet.
I had another look through but cannot find a field for "Next payment due"
From what I know, I'm almost sure it's calculated. Haven't checked if Jason changed that in the last years, but I doubt it.
Here's a bit of PHP that you could use to get the Next Payment Time for a user: https://s2member.com/kb-article/s2eot-shortcode-documentation/#toc-e00e3e46
really would be good to have more paypal data available - please include this