If I analyse your screen shot where you've given "custom" permission to "All user groups".
Users are allowed only for below mentioned content.
You have denied below mentioned permissions to your users. It means users have all permission except below.
If you set it to None, which leaves all of the permissions as "Unspecified" for the All Users group. This approach requires the administrator to specifically assign permissions for only the groups or users that should see the content.
For better understanding about user permission preferences. Pls follow the link.
Another great link to really understand permissions is by Brad Fair. He wrote this fantastic blog that makes this seemingly difficult idea very easy to understand https://www.interworks.com/blog/bfair/2015/09/29/tableau-server-permissions-demystified