push notification private/secrete group doesn't go to all member

I have a private group and when I add a content (e.g. post) via the "create post (context)" block, it sends notifications to only myself (admin) and who posted the note, while other members don't get notifications. Is this a normal behavior because it is private group? I would've thought it should send to all members in the group (provided they are subscribed to ntoifcations, which is the case in my example.

Any help will be appreciated.