Hi Rob,
In most cases, this behavior is caused by a server-side restriction or configuration—such as a security rule, firewall (e.g., ModSecurity), or blocked AJAX request—that is preventing the response from being processed correctly.
Could you please check with your hosting provider or server administrator to see if any security filters, firewalls, or request limitations might be affecting AJAX or POST requests to your site? Additionally, reviewing your server error logs during the time of the pagination attempt might provide further insight.