Argl…I found the bug.
It was an old Redirection-rule, that I placed directly in the server-conf for testing. I forgot to delete it!
I used the one that the permalink-site told me:
—
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
—
All permalinks work. The feed seems the only one that ends in a endless loop…