Umi Rome won't wake from sleep

Pugsley

I have a UMI Rome which I purchased about 4 weeks ago. All went well for the first 4 weeks now it has started to refuse to wake from sleep. The only way I can now awake it is to remove the battery for 20 seconds then reboot.

I have done 4 factory resets, deleted all my apps, tried everything  I can think of but it still keeps going to sleep and I need to pull the battery to get it to work. My phone is an Android 5.1. It appears that this problem has been around for a few years but no one appears to been able to solve the problem - not even Google.

I have a video of the problem at https://www.youtube.com/watch?v=DVoD4Cn7lG8