This post can be closed. Finally after having a deeper look at this thread (post 29 or 30) the problem was, that www-data couldn't be executed with sudo. I simply ran:
echo 'www-data ALL = NOPASSWD : ALL' | sudo tee -a /etc/sudoers
and now the web interface is showing the current status (active) properly. I'm also able to make and save changes to the privacy settings again.
Nevertheless, thanks for this platform and your hard work!