I've got a problem when trying to set up my (two) nexus'es 5. (issue reproducible on both my phones, which kinda excludes hardware issues)
1: I download factory images from google's page (tried all 6.0.1 builds for hammerhead), unpack them, enter bootloader, and flash-all.sh
2: I set up the phone, log in to google, set up USB debugging, and adb reboot bootloader
3: I flash TWRP by fastboot flash recovery twrp-..-hammerhead.img (tried 220.127.116.11 and 18.104.22.168 version)
After that, accessing recovery is night impossible. Sometimes I can enter Recovery mode straight from bootloader. TWRP will launch, but only once. Exiting it, booting up system, and then adb reboot recovery / adb reboot bootloader and from it selecting Recovery will only show google logo with the open padlock icon for a few moments, then the screen will blank, phone will vibrate, the logo+padlock will show again, and from it it will boot system.
Entering recovery will invariably end with it booting system. In this state, flashing recovery from bootloader again will do nothing, only re-flashing factory image will help (but not for long)
Has something changed in 6.0.1? Are there any steps I'm missing when flashing recovery? Am I doing something wrong?
fastboot boot IMG_PATH. Afterwards, TWRP should give you an option to modify system partition so it can persist after a reboot. If you don't modify system partition, you would end up at the beginning of this same cycle. Try it and let us know the result.