Hi,
First, can you specify which version of Android you are using? It should be one of Boundary Devices images:
https://boundarydevices.com/imx6-builds/
Then I don't understand your log, it seems that you type 'adb reboot' from the Nitrogen serial prompt, this is wrong. In the serial output, just type 'reboot'. The 'adb reboot' command should only be issued from your host PC connected to the SabreLite via USB.
Finally, 'adb reboot' is tested and working in all our releases since (at least) KitKat.
Regards,
Gary