Wordpress multisite on different subfolders can't install plugin via network

Question

I have configured a multisite in order to use different subfolder for every site. I have started installing plugins on the network and while the installation works on the main site (https://mywebsite.com/stage/site1 ), nothing happens on the other site (https://mywebsite.com/stage/site2). It happen with theme installation too. It seems the installation are completely independent even if multisite is activated and the correct domain is defined.

What can be the reason of this behavior?

The following code has been used for wp-config.php

define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
define( 'DOMAIN_CURRENT_SITE', 'mywebsite.com' );
define( 'PATH_CURRENT_SITE', '/stage/site1/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

while this has been used for .htaccess

RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /stage/site1/
RewriteRule ^index\.php$ - [L]
    
# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]
     
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

The website structure is:

https://mywebsite.com/stage/site1 (main website)

https://mywebsite.com/stage/site2 (secondary website)

Hope someone can help me to figure it out.

Thank you in advance!