Device says bootloader unlocked but OEM unlock option can enabled and disabled?
It would be good if you enable the Allow OEM unlocking option before proceeding to unlock bootloader
I tried by adjusting the chord into the port and running fastboot getvar unlocked which gave no value meaning the device is still locked (ss attached) 
Even though it says nothing (unlocked : YES etc), I did switch the toggle on for Allow OEM unlocking before proceeding to flash just to be on a safer side and successfully flashed twrp recovery and carbonrom and the device is running well