Hi,
I find a way to correct the issue myself.
For anyone who wants to put his hands in the code:
First, we need to correct the offset issue in the Flexform theme code. In wp-content/flexform/includes/page-builder/composer/lib/shortcodes/blog.php, before the line 118 ($blog_args = array(), put this new line :
$offset = ($paged-1)*$item_count;
This will offset the posts to the right ones.
After that, we need to correct an issue in WordPress 4.4.1 (probably gonna be fixed in 4.4.2) in the canonical URLs. Follow this links to understand and fix the issue :
Explaination: https://core.trac.wordpress.org/ticket/35344#comment:6
Correction: https://core.trac.wordpress.org/attachment/ticket/35344/35344.2.diff
Enjoy!
.