I’m concerned that the explanation say’s the issue is not tied to any particular plugin. Also that it directs readers to two outdated plugins to for testing.
Removing Simple PayPal Shopping Cart resolves the error.
It should also be noted that Health Check is very specific when calling out Simple PayPal Shopping Cart:
Testing wordpress-simple-paypal-shopping-cart: The loopback request to your site failed, this may prevent WP_Cron from working, along with theme and plugin editors.
Error encountered: (0) cURL error 28: Operation timed out after 10001 milliseconds with 0 bytes received
All other plugins report: “The loopback request to your site completed successfully.”
Still, Simple PayPal Shopping Cart is otherwise a GREAT plugin, beautifully executed.
I have no intention of removing it unless I have to and continue to look for a solution.