I get this issue every now and then whenever an update is requested to be installed, but I don't install it and then the battery drains up. I figured it doesn't depend on the device (I had it happen on different devices, and it behaved this way).
Holding power button (I think I also pressed volume down, not sure if this is the way to power down pixel) and booting up again several times helped eventually.
Once I had a weird bug when it booted to the main profile lock screen, and then kept going back to the graphene logo as soon as network was discovered and it went on and on.
I suppose I was just lucky to be able to boot up eventually - so perhaps such battery-drain power off shouldn't be treated as a reboot that proceeds with installing an update, and some separate "ok to update" flag should be set when the phone is rebooted gracefully?