Facebook has strict limitations on how posts and insights are available for Facebook Groups. Thus, you cannot see insights for a Facebook Group in Hookle.
How to see insights for posts?
To be able to see the post's insights (and publish to a Group) you need to be Admin of that specific Group and authorize Hookle as an App on your computer.
Is your Facebook Group connection alive?
Unfortunately, sometimes the connection to your Group account is expired and thus the insights are not visible anymore. To fix that, try to reconnect the account.