This issue can happen for a number of reasons.  The first thing to ask is who cannot see this page?  If you find it's a user like a Parent, Student Or other Role based users the best place to start is in Group Page Access.  Check the to ensure the proper access is set via Core > Security > Group Page Access.  There you can check to ensure the proper access is set for the group type experiencing the issue.

Another common problem is a task on one of the roles the user has is unchecked.  

This is most common on the All School Role.  There are several tasks in this role that have to be active for users, even with a Manager role, to have access to the group pages. They are as follows:

View Course Page
View Activity Page
View Advisory Page
View Alumni Page
View Team Page
View Community Group

If these tasks are unchecked on the All School Role, no user in the system will be able to view the group pages.  

To check this navigate to Core > Security > Roles >  Locate the All School Role and select it.  Click Tasks on the right and check to make sure the above tasks are checked as Active as seen below.

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