When you grant a group of users access to a line, they gain access to all the sensors currently on that line. However, if you add another sensor or view to that line in the future, it will not be automatically added to the group with line access.
To resolve this, go to the Administration panel, then select Groups, and locate the group lacking access. A dialog will open, and at the bottom, you'll find "Show sensors not in this group". The new sensor/view will be listed there. After you've added it, the users should immediately gain access to the new sensor or view.