Final answer:
The most common problem encountered with a bag-valve-mask device is the failure to seal the mask properly over the victim's mouth and nose.
Step-by-step explanation:
The most common problem encountered with the use of a bag-valve-mask device is the failure to seal the mask properly over the victim's mouth and nose. When using a bag-valve-mask device, it is crucial to ensure a tight seal between the mask and the victim's face in order to deliver the appropriate amount of air. If the mask is not sealed properly, air may leak out, reducing the effectiveness of the device.