In my case it is the plugin RestroPress which creates the same issue.
I’ve found out by de-activating one by one the plugins and checking the health of my site.
After de-activating restropress the health was just fine.
I have written them an e-mail and now awaiting there response.
Men this was a long road of searching and solving problems, and placing back back-ups.
Health Issue !
Your site could not complete a loopback request Performance
Loopback requests are used to run scheduled events, and are also used by the built-in editors for themes and plugins to verify code stability.
The loopback request to your site failed, this means features relying on them are not currently working as expected.
Error: cURL error 28: Operation timed out after 10001 milliseconds with 0 bytes received (http_request_failed)
