Update WordPress menu problem

Hello,

I’ve a problem when i need to update the menu of my website. I don’t use some plugin to make my menu, it’s a core part of WordPress and not added by the theme.

Wordpress and all my plugins are up to date :

Wordpress 4.9.4
Theme : Genesis with the child theme Education

plugins :
Advanced Custom Fields Multilingual
Advanced Custom Fields PRO
Better Font Awesome
Cookie Notice
Custom Post Type UI
Duplicate Post
Genesis Responsive Slider
Genesis Simple Edits
iThemes Security Pro
Regenerate Thumbnails
Responsive Lightbox
SiteOrigin Page Builder
SiteOrigin Widgets Bundle
TinyMCE Advanced
User Role Editor
USM Premium
WP Mail SMTP
WPML Media
WPML Multilingual CMS
WPML String Translation

So, when i need to update my menu (by clicking on the save button), i’ve an internal server error page and my menu isn’t updated.

I’ve tested many things and i’ve changed my php.ini configuration to increase some limits (size, time, etc.) and after some tests, i’ve found that deactivating the WP Mail SMTP plugin, i can update my menu!

By viewing my list of plugin and knowing the theme i use, have you got an idea to solve the problem? Why is there a conflict with the WP Mail SMTP plugin juste by updating the menu with the WordPress core?

Thanks for your help and have a nice day!

PS: sorry for my english (french here >.<)