Can’t fix “Fatal error: Uncaught Error: Call to undefined function wp()”

Hi,

Here is my WordPress configuration :
PHP/MySQL : 7.0 / MySQL 5.7
Theme : Avada
Host : OVH Mutu perf2014x1
Website : https://mapatisserie.fr/

Since yesterday morning, all my pages were blank with 500 HTTP error. My wordpress is working fine for more then 2 years. I activated the ? developpement ? mode (an option when you are hosted by OVH) and I could see this error :
Fatal error: Uncaught Error: Call to undefined function wp() in /home/xxxxx/www/wp-blog-header.php:16 Stack trace: #0 /home/xxxxx/www/index.php(17): require() #1 {main} thrown in /home/xxxxx/www/wp-blog-header.php on line 16

I googled and try to :
– remove .htaccess : changed nothing
– renamed all extentions : changed nothing
– renamed the theme : changed nothing
– do a wordpress manual update to refresh all files : changed nothing
– restored a D-1 and D-2 backup : changed nothing

that’s very strange, none of my actions fix anything. I even add the ? die(); ? at the beginning of the index.php file: nothing changed !

Even worst : I upload 2 files on the root web directory “www/” : test.html and test.php. I can display the content of the .html file but when I try to display the test.php, got a strange ? File not found. ? while I’m sure of the URL and there is no link with WordPress ! ??

So, if it’s not PHP, html or images works : https://mapatisserie.fr/wp-content/uploads/2015/08/recettedebiscuitmadeleine1.jpg

Any hint to try to find the issue is welcome, thanks !

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