Over the last year I've had a few experiences where 7a's and 8a's have gone into boot loops. The general pattern appeared to be extreme depletion of the battery and when I did manage to the device back to a normal boot, there was evidence each time that some sort of update was/is in progress.
The most recent occasion was in the last days. The device, at a momentary glance in the main screen was showing 100%. But the boot looping continued. Attempted pauses at boot as some have suggested in this forum. I selected recovery, trying to reboot all sorts but was then continually arriving at the inebriated green android with its chest open.
Here's my mistake, when you get to the robot, with the "no command" don't assume it's a failed state and attempt to reboot yet again. No. no. Put the phone down and leave it charging for a good long while. Let it do what it's got to do and it will (likely) restart. Perhaps, after an hour if nothing has happened, try and reboot and something else, but once again, wait at the robot and give it a chance to boot.
Best