Problems with notification mails


I’m using the latest nextcloud version and have problems with the notification mails. In the configuration of all users I have configured to get mails if file or folder are changing.

User2 do get an notification mail if user1 creates a new folder an shares this folder with user2. But after this, if user1 or user 2 uploads new files into this direcory or create a new subfolder the other user do not get any notification mail.

What could be the reason for this?