I don't have an answer for you, but I'm convinced something on PayPal's end changed within the last month or so (unless there was some major change to all webhosts). If you look around this forum, you'll see that many of us are experiencing the same issue with IPN. I haven't looked at my server logs like you. Maybe I'll do that today. My IPN Listener always logs to the database when it's "hit" with a POST. The last successful log was Sept. 5. However, the IPN Simulator works, and I see those logs from the Listener. But anything from PayPal's production IPN does not even show up in my logs. If you look at the WooCommerce forums, you'll see there's a lot of people there with issues, too. I'm using PrestaShop, so you can see that it spans different eCommerce suites.
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