Plugin took site down after a week or so

Hi there.

Thanks for this plugin.

It worked fine for past week or so. But today our site went down due to the plugin. Here’s some error log info that might be helpful.

[Tue Sep 19 07:21:25.998753 2023] [proxy_fcgi:error] [pid 22494:tid 140021981939456] [client 112.213.42.15:0] AH01071: Got error 'PHP message: PHP Fatal error:  Uncaught Error: Call to undefined function shell_exec() in /home/608767.REMOVED.com/gpnhmcjwnz/public_html/wp-content/plugins/dynamic-front-end-heartbeat-control/heartbeat-controller.php:408\nStack trace:\n#0 /home/608767.REMOVED.com/gpnhmcjwnz/public_html/wp-content/plugins/dynamic-front-end-heartbeat-control/heartbeat-controller.php(419): get_system_load_average()\n#1 /home/608767.REMOVED.com/gpnhmcjwnz/public_html/wp-settings.php(462): include_once('/home/608767.cl...')\n#2 /home/608767.REMOVED.com/gpnhmcjwnz/public_html/wp-config.php(103): require_once('/home/608767.cl...')\n#3 /home/608767.REMOVED.com/gpnhmcjwnz/public_html/wp-load.php(50): require_once('/home/608767.cl...')\n#4 /home/608767.REMOVED.com/gpnhmcjwnz/public_html/wp-admin/admin-ajax.php(22): require_once('/home/608767.cl...')\n#5 {main}\n  thrown in /home/608767.REMOVED.com/gpnhmcjwnz/public_html/wp-content/plugins/dynamic-front-end-heartbeat-control/heartbeat-contr...', referer: https://www.REMOVED/garden-store/filters/use/pasture/

It causes an Apache server error, which standard server message:

Service Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.Apache/2.4.57 (Debian) Server at www.mckaysgrassseeds.com.au Port 80

After host did something with the services on the server, WordPress started to load again, but showing it’s critical error page:

There has been a critical error on this website

The only way to prevent that was the disable the plugin (renaming its folder).

Any thoughts?

Jonathan