This is a known issue in the V4S Kiosk application, if a volunteer has canceled his Sisgnup from Salesforce, the volunteer name is removed from the Job/Shift details screen, but it remains on the volunteers today screen.
i.e., If the Salesforce administrator has changed the volunteer Status from confirmed to canceled and then deleted the volunteer hours of the volunteer in Salesforce, that volunteer name is removed from the Job/Shift details screen automatically. But, the volunteers today screen still shows the volunteer name with a Check-in button.
The tech team is working on this issue, and the volunteers today screen will be auto refreshed upon volunteer status change and automatically remove the canceled volunteer names from the volunteers today screen. This feature will be implemented in the next release of the V4S Kiosk application.