“Debug Information” tab empty

Using WP 4.9.9 and Health Check 1.2.5. I have enjoyed this plugin many times on many sites for collecting information and finding problems.

My problem: The “Site Status” works as expected (info below). But clicking “Debug Information” tab grinds away for 15-30 seconds, but then leaves an empty page. (The other tabs – Troubleshooting, PHP Information, and Tools show the expected content.)

Any idea what might cause this? What additional information could I provide to troubleshoot this? Many thanks.

WordPress Version 	4.9.9 - We were unable to check if any new versions are available.
Plugin Versions 	

    Your site has 21 active plugins, and they are all up to date.
    Your site has 8 inactive plugins, it is recommended to remove any unused plugins to enhance your site security.

Theme Versions 	

    Your site has 5 installed themes, and they are all up to date.
    Your site has 2 inactive themes. To enhance your sites security it is recommended to remove any unused themes. You should keep twentyseventeen, the default WordPress theme, astra-child-LLL, your current theme and Astra, the parent theme.

PHP Version 	7.0.33 - For best performance we recommend using PHP 7.2 or higher.	
Database Server version 	5.5.60-MariaDB
- For performance and security reasons, we strongly recommend running MariaDB version 10.0 or higher.
PHP Extensions 	All required and recommended modules are installed.
MySQL utf8mb4 support 	Your MariaDB version supports utf8mb4
HTTPS status 	You are accessing this website using HTTPS.
Secure communication 	Your WordPress install can communicate securely with other services.
Scheduled events 	No scheduled events have been missed.
Plugin and Theme Updates 	

    Plugin updates should be working as expected.
    Theme updates should be working as expected.

HTTP Requests 	HTTP requests should be working as expected.
REST API availability 	The REST API is available.
Communication with WordPress.org 	WordPress.org is reachable from your server.
Background updates 	

    The WP_AUTO_UPDATE_CORE constant is defined and enabled.
    No version control systems were detected.
    Your installation of WordPress doesn't require FTP credentials to perform updates.
    All of your WordPress files are writable.
    WordPress security and maintenance releases are blocked by define( 'WP_AUTO_UPDATE_CORE', false );.

Loopback request 	The loopback request to your site completed successfully.