If you are using Jetpack Publicize (for automatically post to Google+ page), then you will be encounter the same problem here. By default, the posting will be set as shared privately. Meaning, the post on Google+ page is visible to you only!
Solution
1. Navigate to below URL link of Google+ page,
https://plus.google.com/apps
2. Under the Apps tab, click on Edit and change the Visible to Public.
