Clickbank niche Storefront messes with Rest API

Hi
With this plugin activated, Site Health reports

The REST API request failed due to an error.
ERROR: [] cURL error 28: Operation timed out after 10000 milliseconds with 0 bytes received

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 10002 milliseconds with 0 bytes received

I’ve read that it’s normally a server problem, out of date PHP and cUrl. So I updated them to the latest stable versions. I also increased the memory limit, both make no difference while the plugin is active. The only other error message from Site Health appears when the plugin is inactive – telling me to remove inactive plugins.
I also read on here somewhere amongst the cUrl error 28 posts that it can be caused by PHP sessions not being stopped. I’m not a PHP expert and so can’t tell whether the session that appears in the plugin’s code is ended or not.
I’m hoping someone can sort this as both this plugin and the similar named Clickbank Storefront would be fantastic if they worked.