There are several situations why this will happen.

Device moved
Devices get moved around in office environments due to the need of features or changes in office structure. When a device gets moved, it is possible it will stop collecting because the device may be using a dynamic IP scheme, getting a new IP address at the new location. Or, it is possible the device is being used on WiFi now compared to a wired connection before which uses a different MAC address.

• If New IP address is used, make sure the Data Collector includes that IP range
• If New MAC is used, contact support with new MAC information

Service
When service happens on a machine it is possible that important components are replaced that include the identity of the device. For example, when a formatter gets replaced the networking parts are then changed giving the device a new MAC address even though the IP may be the same.

• Contact support with network information of the device, including the MAC address