Tools – Health Check – Shows Your site cannot complete a loopback request

This only happens when the Salon Bookings plug-in is activated. If I de-activate it, no critical issues under Tools – Health Check. I searched the web and forums and didn’t find anything about it. The exact text of the error is:

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)

The page I need help with: [log in to see the link]