i've created a multisite network with subdirectories. (Before i set permalinks on postname.)

When i create a new subsite, the dashboard looks like the css files cant be loaded. (an whitescreen with links.)

If i visit the new site's homepage, it seems ok. Also 404 errors if i want to access any backend-sites of any created website.

www.mynetworkdomain/website/ = works fine.

www.mynetworkdomain/website/example-page/ = works fine.

www.mynetworkdomain/website/wp-admin = dont work.

All backend sites dont work. (404)

I think, it's an .htaccess or an permalink problem, but i cant access the new subsites Dashboard. On my main site's dashboard everything works fine!

What can i do to use my subsites backends correctly?

I would be very glad if you can help me.

Thank you very much. <3

.htaccess:

RewriteEngine On
RewriteBase /
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 \[L\]

• wp-config and htaccess is okay.
• tried to reinstall the whole network.
• de- and activated nginx.
• checked the php settings and increased limits to maximum
• tried it in different homenetworks
• An very interesting fact is: I've changed the URL from my subsite to an completely other main URL on my server. Suddenly the wp-admin dashboard's GUI looked normally! But the links wont work anyway. (Site not found)