When you share content from one group to another (in this case from an open group to an externally accessible group), that content is not visible when you view that group through the mobile app (iOS v3.3.4 (38) on iOS 9); only content that lives natively in the group is visible.
(This is likely related to the open bug around search-based filtering in the group not considering content that is shared to the group.)
I have tested this and reproduced the issue on my site and therefore filed a bug for the issue. The bug id is JIVE-62114, if you would like to be notified when the bug is resolved, feel free to create a case in your private support group and provide the Bug ID to the case and a Support member will accept and notify you when the bug has been resolved.
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