Try adding your email as bcc to a run so you can confirm the 50 emails are being generated by the system. Then at least you know the issue is downstream.
if they dont generate then confirm the users are definitely part of the group sometimes user imports can overwrite their group access if they appear multiple times.
Set them up individually and check they go out as individuals you might get a more detailed log record.
In order to be a NPrinting report recipient user needs to have a role in NPrinting. Make sure all people from 50 are at least "Users" or "NewsStand User" or have any other role which allows them to receive reports.
Also do what Andy suggested regarding groups.
On top of that double check whether those users have filters created for them (user filters) which could interfere with your current report.. If they have, make sure those filters are created in seperate NPrinting app on separate connection.
let us know how it goes