Backoffice (admin editor) display problem

Hi,
Here is my problem :
WP works well, but doesn’t display all things correctly in the admin area.
For example : with the Contact Form 7 plugin, normally, in the configuration of a form, I should have tabs “Form | Mail | Messages | Additional Settings”, like in this screenshot : https://ps.w.org/contact-form-7/assets/screenshot-1.png?rev=1176454
But unfortunately, this tabs are displayed as simple links with anchors on a single page.
Drag n drop doesn’t display correctly too.
It’s not a blocking point for this plugin, but I’ve the same problem with Gantry 5, problem that restrain a lot the use of this framework.

Screenshots of the problems :
Broken Contact Form :
https://frama.link/MHM-NGxE
Broken Gantry :
https://frama.link/xDw0wkaH
Gantry should display as this :
https://frama.link/c3N9PNgz

My configuration :
PHP : 7.2
WordPress : 4.9.8
Plugins : Askimet, Classic Editor, Coming soon page & maintenance mode, Contact Form 7 and Gantry 5.
(same on my localhost and no problem, problem only on the production server. The only difference is that I work with MariaDB on the localhost, and MySQL on the distant server.)

I’ve tried to disable/reenable the plugins.
I’ve tried to disable the .htaccess.
I(ve tried to add define( ‘CONCATENATE_SCRIPTS’, false ); in the config.php
…but nothing works.

Does someone have an idea to help me ?
Thank you by advance