I installed and activated the plugin fine on my own site which is also hosted at Siteground.
I created a staging version of the site experiencing the problem. I switched the theme to Twenty-Twenty-Three and with all of the other plugins disabled I still had the same problem.
The site that is having the issues uses a Sucuri firewall so the traffic is somehow routed through them. That’s the only difference I can think of between the sites where the plugin works fine and where it doesn’t.
I’ll try changing the DNS records for the staging site so that it doesn’t involve Sucuri.