I was almost ready to give up on the Nubia - already had given up on it.
But then today I put it up for charge and lo behold! The notification LED
started blinking in an SOS pattern. So I googled the internets, and found
similar cases for various brands of mobiles. I let the phone charge on.
There was nothing on the display yet.
Then on one post someone mentioned that they had more luck with a 2.4A
charger. I remembered that I had one microUSB power adapter I had purchased
for my Raspberry Pi3. So I plugged in the phone to this 2.4A 5V adapter.
And suddenly the charging animation showed up. I cannot explain my joy!
Then I let it charge till 20% on it. After I used normal 1A charger to
fully top up.
And now the Nubia Z9 mini is back!!!