Private contributions visible to others

[sushidave]

Describe the bug
Private contributions seem to be visible for others, at least for the user's followers.

To Reproduce
Steps to reproduce the behavior:

1. Create a contribution.
2. Set visibility to private.
3. Publish.
4. Followers get a notitifaction and are able to see the contribution.

Expected behavior
Private contributions should stay private, i.e. neither should followers get a notification nor should other users be able to see those contributions.

Additional context
Reported by user Hannelore (AT), see https://alpha.human-connection.org/contributions/das-ist-ein-test.

[applelore]

User Hannelore H., Österreich, reported another case where private visibility didn't work, see https://alpha.human-connection.org/contributions/erste-schritte-praktische-anleitung-fur-neueinsteiger. Followers were able to see the contribution and to insert their comments (see the first two comments of the contribution).