When Chwala is configured to use webdav driver:
[19-Feb-2016 18:10:50 UTC] PHP Warning: require(SabreDAV/vendor/autoload.php): failed to open stream: No such file or directory in /usr/share/chwala/lib/drivers/webdav/webdav_file_storage.php on line 25
[19-Feb-2016 18:10:50 UTC] PHP Fatal error: require(): Failed opening required 'SabreDAV/vendor/autoload.php' (include_path='/usr/share/chwala/lib/drivers/webdav:/usr/share/chwala/lib/drivers/seafile:/usr/share/chwala/lib/..lib:/usr/share/chwala/lib/..lib/ext:/usr/share/chwala/lib/..//lib/client:.:/usr/share/pear:/usr/share/php:/usr/share/roundcubemail/program/lib') in /usr/share/chwala/lib/drivers/webdav/webdav_file_storage.php on line 25
A simple fix is to change the path in require to 'Sabre/autoload.php', so it will use packaged version of the SabreDAV lib, but this does not match the Sabre libs installation described in Chwala's README.