I resolved temporary the problem with this little modification :
In the shortcodes.php file, I replace the fonction by this one:
function tx_button_function($atts, $content = null) {
$atts = shortcode_atts(array(
'style' => '',
'text' => '',
'url' => '',
'color' => '',
'textcolor' => '',
'target' => '',
'class' => '',
), $atts);
$return_string ='';
$return_string .= '<a href="'.esc_url($atts['url']).'">target="'.esc_attr($atts['target']).'">'.esc_attr($atts['text']).'</a>';
return $return_string;
In the button generation text, I added this attribut at the end : target=”_blank” to get an open link in new window.
Example : [tx_button style=”default” text=”Google Maps” url=”https://maps.google.com/” color=”#1e73be” textcolor=”#ffffff” target=”_blank”]