That can happen if the view is attached to a view group that is disabled in Stratum.Viewer. A view group can be made active again using its Active property.
That also can happen if you are a view or security administrator and the view group you selected for the view is not one that is enabled for your user profile group. If that’s the case, the group needs to be enabled for your user profile. Otherwise, just select a different view group for the view and be sure it is one that already displays in the left panel.*
*Note: If you are a casual or advanced user, the only view groups you can save views to will be active view groups already enabled for your user profile.