pre_clear_scheduled_hook

add_filter( 'pre_clear_scheduled_hook', function( $null, $hook, $args, $wp_error ) {
	$core   = apply_filters( 'boldgrid_backup_get_core', false );	
	$logger = new Boldgrid_Backup_Admin_Log( $core );
	
	$logger->init( 'pre_clear_scheduled_hook.log' );
	
	// We want to include the trace to see what is clearing the schedule.
	$e = new \Exception();
	$e = explode( "\n", $e->getTraceAsString() );
	
	$logger->add( print_r( array(
		'$hook'     => $hook,
		'$args'     => $args,
		'$wp_error' => $wp_error,
		'$e'        => $e,
	), 1 ) );
	
	return null;
}, 10, 4 );