Thanks for your help.
I turned debugging up to full but moodle returned no additional errors. I then had a look through our error logs and saw some warnings about the exec() and shell_exec functions being disabled.
I'm running PHP-FPM so I looked through my PHP-fpm settings on WHM for each account and in the disabled functions section, neither said that these functions were disabled.
I then found this resource Enable exec() with PHP-FPM - Slurp-Ramen.com.
I found via the command line that these functions were being disabled. I removed them from the function disabling line, restarted the PHP-FPM service and we are in business.
These functions are disabled for all accounts by default by PHP-FPM in this file:
You can prevent them from being disabled there too.
Had this issue for ages now. Over the moon.
Thanks for the help.