New user added to a group does not have access to group-shared files

help

#1

Steps to reproduce
1. Share a folder with a group
2. Add new user to group
3. Login as new user and try to access any shared file

Expected behaviour
File opens / download starts

Actual behaviour
Error message when clicking on a shared file.
For example a PDF:

PDF.js Version 1.1.469 (build: f06aa6a)
Nachricht: Unexpected server response (500) while retrieving PDF
DOCX: ERR_INVALID_RESPONSE in Chrome Browser

Server configuration
Operating system: Debian Jessie
Web server: Apache2
Database: MySQL
PHP version: 5.6.28
ownCloud version (see ownCloud admin page): 9.1.3 (stable)
Updated from an older ownCloud or fresh install: Updated from 8.0.3 (via regular upgrade path)
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption): server-side-encryption

ownCloud log (data/owncloud.log)
(IP, filepath and username replaced)

{"reqId":"yd3xqPcCPtZX9um1kjz9","remoteAddr":"<IP>","app":"no app in context","message":"Can not decrypt this file, probably this is a shared file. Please ask the file owner to reshare the file with you.","level":3,"time":"2016-12-15T09:59:45+00:00","method":"GET","url":"\/index.php\/core\/preview.png?file=<filepath>&c=1e3ae3bc2ec0b9934b95843a4e309d2b&x=32&y=32&forceIcon=0","user":"<username>"}

Integrity status for oC9+

No errors have been found.

Apache error.log

 PHP Fatal error:  Class entry requested for an object without PHP class in /var/www/owncloud/3rdparty/icewind/streams/src/CallbackWrapper.php on line 108
child pid 2004 exit signal Segmentation fault (11)

#2

From the documentation:

Share owners may need to re-share files after encryption is enabled; users trying to access the share will see a message advising them to ask the share owner to re-share the file with them. For individual shares, un-share and re-share the file. For group shares, share with any individuals who can’t access the share. This updates the encryption, and then the share owner can remove the individual shares.

-> https://doc.owncloud.org/server/latest/admin_manual/configuration_files/encryption_configuration.html#sharing-encrypted-files