You've just seen a dramatic increase in traffic on the VLAN used by mobile devices at your company. You are aware that there haven't been many new mobile devices. What might be the problem here?

The likelihood that there is malware on the system and that malware is exploiting your network to carry out some action is the most likely explanation for a sudden, significant rise in network traffic. Since the mobile devices are on a VLAN, your main network isn't being directly impacted. The source of the network traffic must be identified right away, and malware needs to be removed. It's unlikely that a malfunctioning mobile device is the root of the issue. It is unlikely that your monitoring software is infected. Your monitoring software should be designed to detect incidents involving high network traffic. Limited connectivity would not present as an increase in network traffic.