Due to some recently introduced applications that required a custom PHP setup, I have switched to Apache with PHP-FPM instead of mod_php.
Now, I don't get SabreDAV working again and I can't find what is going wrong as it displays no errors in the Apache log.
When I open the URL of the server in my browser and log in as admin via HTTP authentication, I just get a blank page rather than the file browser. (I confirmed with var_dump that $user is 'admin' so the authentication is still working)
And the client RoundCube (with the MyRoundcube CardDAV plugin) is giving me an error without actually stating what is going wrong.
I hope you will be able to help me to track down what is actually going wrong, since I am unable to find any clue in the logs.