Gravity form won't display manually

I'm using Gravity Forms with Wordpress, and I got a problem :

When I insert manually a form in a post, it won't display it. Instead I have this :

(...) pariatur. Excepteur sint occaecat cupidatat non proident, sunt in 
culpa qui officia deserunt mollit anim id est laborum.

[gravityform id="13" title="true" description="true"]

But, If I embed this form in php, it works perfecty!

gravity_form('13', true, true);

I need manually displaying to work in order to let my client manage his forms as he wants.

Everything is up-to-date, I don't use plugins except Polylang which is not causing conflict regarding the System Status.

Any ideas?

Thanks in advance :)

EDIT :

I was using themosis for this project. Themosis have a conflict with plugins as Gravity Forms. More info here :)

https://github.com/themosis/framework/issues/220

Solution

// Try to add a shortcode in you theme's functions.php file if its the only occurance!
function gravityform_func($atts) {
    $args = shortcode_atts( array(
        'id' => null,
        'title' => true,
        'description' => true,
    ), $atts);

    return gravityform($args['id'], $args['title'], $args['description']);
}

add_shortcode('gravityform', 'gravityform_func');

WordPress shortcodes are built in WordPress functionality. If they aren't working there is something else going on with your WordPress install. The first thing to do is to check for possible plugin or theme conflicts.

Activate the default WordPress theme and test to see if the shortcode works

If it does then something in your theme is causing the issue. If it doesn't then:

Deactivate ALL plugins
Activate only Gravity Forms
Test the shortcode

If it works then another plugin is causing the issue.

Activate each plugin one by one
Test the shortcode after each plugin is activated

Also make sure you insert the shortcode in the post editor in HTML mode and then update your page. Shortcodes are native functionality to WordPress so something is preventing WordPress from parsing the shortcode.