I installed CM 14.1 on a Nexus 6 and the first update booted into TWRP automatically to install but failed.
I manually installed the zip from the cmupdater folder and rebooted.
Now every time I try to reboot my phone or power it on from powered off it goes straight into TWRP.
Currently I have to boot into the bootloader and choose the
Start option to get into my system.
Tried clearing dalvik/cache & internal storage in case something was cached somewhere. No dice.