Hi,
See below:
1. Is your SITE URL and WordPress URL the same? You can check in Settings->General. If they're different move your WordPress files into the site URL. Sometimes having them different causes issues.
2. Try turning off IPN on your PayPal account. Remove the URL and disable it. This does not mean IPN is OFF per say. It will get its IPN information from WooCommerce which will accurately pass the correct IPN URL.