Nexus 7: Unable to install factory image, stuck in < waiting for any device >

I want to restore factory android on my Nexus 7 2012 WiFi. I'm following the official guide . I start the device in fastboot mode by executiong: adb reboot bootloader This works well. But **when I run any command that uses** fastboot **the execution gets stuck**, eg: $ fastboot oem unlock The same issue with flash-all.sh. I also noticed that if I run adb devices it doesn't list the tablet. However it gets listed if I run the same command after entering Recovery Mode (I have TWRP recovery). **More details/preconditions:** I used to have CianogenMod on the device but I smashed it by mistake (I removed Android in recovery mode instead of simply wiping the data). I can't find the CianogenMod image anymore on LinageOS site (there is only Nexus 2013 available) so I'm trying to install at least what is available.