Hi,
Thanks for your feedback, please follow the steps below:
1. Select one group
2. Click "Select All" button (then all contacts in the group will be selected)
3. Then it shall work
Maybe we shall improve the app a bit, when you click one group then by default all contacts in the group will be selected? But maybe sometimes you are just want to look at the contacts inside the group...
Let me know if there is still any issue.