You can try setting debug mode in src/config.php if it's making it that far:
$config['debug'] = true;
That may expose an error message, though it depends when the issue is happening.
Otherwise, you may need to enable display_errors
in your php.ini to see if that outputs anything. (Alternatively, you may need to set PHP's error_log
to a file to ensure that fatal errors are logged there to try to get to the bottom of this.)