Groups using the Mobile App> Reachable filter in their query may not pull in the expected number of users.
- Classic Studio | Manage| Groups
It's expected mobile app users that have current records which indicate they would like to receive push notifications will be included in the group.
There is currently no known workaround or resolution for this issue.
Please check the current status of this issue on the Known Issues Tracker. (Issue ID: MAGIC-6380)