site health problems after wp update 5

Hi,
after the big update to wp 5 the site health is flagging critical errors. With the aid of plugin ‘site health’ I came to find that ‘wp image refresh’ is the culprit. It causes the following error:
‘Your site could not complete a loopback request
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 10000 milliseconds with 0 bytes received (http_request_failed)’
As the plugin is a crucial component for the site, I cannot disable it.
Please help.
Uli

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