I run a server hosting multiple WordPress installations with the iThemes Security Pro plugin installed. One of the things that this plugin does is it uses Sucuri SiteCheck to scan the site for vulnerabilities: https://sitecheck.sucuri.net/
Recently, SiteCheck has been failing on all of my sites, reporting the following error:
Unable to properly scan your site. Timeout reached
Coincidentally, the new Site Health WordPress Tool has also been reporting the following error on all my sites:
The REST API is one way WordPress, and other applications, communicate with the server. One example is the block editor screen, which relies on this to display, and save, your posts and pages. The REST API request failed due to an error. Error:  cURL error 28: Connection timed out after 10000 milliseconds
I suspect that the issues are related, but I don't know where to start to fix this issue. I have both Fail2Ban and ModSecurity enabled on my server and on Apache respectively, but the problem still persists when I turn off the services.
Will appreciate if someone could help pinpoint possible issues. SiteCheck has always worked on my server without a hitch.