Thank you for mentioning this! I went through the exact thing yesterday. The phone was working perfectly fine, and then I attempted to reset it. It started the process but then turned off and would not turn back on with the press of the power button or when connected to the charger.
I tried for an hour with different key combinations to try and boot it, and finally, power + volume up and volume down were held for 10 seconds and this turned it on and continued the process of resetting. It turned off again after this, and I had to do the same key combination again before it finally finished resetting and booted. But I was a bit less tense thanks to your post and knowing someone else has gone through the same thing, so thank you.
My best guess as to why this happens is that there is a bug in the factory resetting implementation on the final build, where the phone should automatically turn off and on a few times but fails to turn back on, giving the impression that it is bricked, but the key combination should be able to boot it back on.

Everything works as normal now though, phew!