Just in case if someone else runs into this problem:
After a failed update attempt, my Likebook Mars just got stuck in the 'Starting UP' screen, attempts to boot into FASTBOOT failed even after selecting such option in the recovery mode (if your device show a screen with 'No Command' just long press again the button in the small hole to access the recovery mode). Every time that 'booted' got recognized as ADB DEVICE by the Android Tool, that makes the device not being able to apply the update again.
I fixed this by utilizing Android Platform Tools (
https://developer.android.com/studio...platform-tools).
Just open a windows command prompt on the folder with the APT and run the command 'ADB reboot fastboot'.
After that, the Android Tool recognized the device again as a LOADER DEVICE and allowed me to try to apply upgrade again. This time it succeded and my Mars is now running Android 8.1.
English is not my primary language, sorry if something does not make much sense.