Unable to register module

I have built a simple child module which I cannot seem to get to activate. I’ve followed the API instructions very carefully.

I’ve created a directory under plugins/bwp-google-xml-sitemaps-modules and placed my module there: page_arg.php. I’ve registered this directory under Site Options | Custom module directory.

The php file writes text to a file when it’s called and the file isn’t being written so I’m certain it’s never getting loaded. Is there something else I need to do to register the module?

Here is the module code:

<?php

/**
*  Module calls parent then finds fields-hub entry and sets high priority
*/

add_action('bwp_gxs_modules_built', 'bwp_gxs_add_arg_module');
function bwp_gxs_add_arg_module()
{
    global $bwp_gxs;
    $bwp_gxs->add_module('page', 'arg');
}

file_put_contents('~/test.txt', 'CALLED');

class BWP_GXS_MODULE_PAGE_ARG extends BWP_GXS_MODULE_PAGE
{
	public function __construct()
	{
		// @since 1.3.0 this is left blank
	}

	protected function generate_data()
	{
		
		parent::generate_data();
		
		for ($i = 0; $i < sizeof($this->data); $i++)
		{
			$data = $this->data[i];

			if (strpos($data['location'], 'fields-hub') > 0) {
				$data['priority'] = 1.0;
				$data['freq'] = 'daily';
				$dateTime = new DateTime($myDate);
				$formatted = $dateTime->format("Y-m-d\TH:i:s.z\Z");
				$data['lastmod'] = $formatted;
				$this->data[i] = $data;
			}

		}

		// always return true if we can get here,
		// otherwise we're stuck in a SQL cycling loop
		return true;
	}
}