You may see this on the Add Single / Add Multiple volunteers function that you get to from the First Time Volunteer link.
You may have entered Volunteer information in the add individual/multiple volunteer screen. But if your mobile/tablet screen gets locked before the data is saved, the contact information does not get Saved. So when you unlock the screen, you will NOT see that data that you had previously entered..
If you are going to be entering new volunteers, please make sure that the Sleep Time on your mobile device is set to a higher value, so that it does not lock automatically when you are entering data. Please make sure that the data is saved before the mobile/tablet screen is locked.