Here are some more information and screenshots to specify the situation: The folder GKK is created and shared by the user Support. The AD group AlleGKK has permissions to read and edit. But the user is not able to see this folder when she is a member of that group.
If the user is removed from the active directory group AlleGKK and manually get permissions to edit and share that folder it is visible again.
Our server is running 9.0.2. The user does not have any files or folders. When running the files:scan -vvv with the userID I get 3 folders (root, /files and /cache). The user is assigned to the group correctly. Just does not see the shared folder. Like visible in the screenshots: The user does see the folder when the permission is added directly for the user.
Did not look into the logs yet... but will do it now.
I think the ownCloud 9.0.2 version you're running is highly outdated. Maybe you can consider to use a recent one to avoid such situations in the future?