This is an issue which comes up during the setup process or installation process of converting your machines to a CloudReady machine. You may notice this issue on your my.neverware.com account in the "Devices" section or on your Google Admin Console where the device details are listed. Below, you will find the two common reasons as to why this issue may occur:
1) During a mass deployment process, no matter which deployment tool is used, the image has to be captured before you boot the device. If you boot the device before capturing the image it will write it's MAC address to the file and save it as a licensing address. This leads to capturing the image with the MAC address and thereby deploying images with a pre-set MAC address.
2) If you are connecting to a network via a USB dongle or any other USB ethernet adaptor while the USB installation process is underway, the device again writes its MAC address as that adaptor's MAC address. Following this, every other machine that is installed using this same USB installer will have a preset MAC address of the first device.