Replaced the Digitizer, iPad Mini 16gb Randomly Shuts off

Hello Everyone,

I own a repair store for about 9 months now, fixed everything that came by from android to iOS. So I'm not a novice in this.

Last week a customer brought to me 3 iPads for repair. 2 iPad minis and an iPad 3. Fixed all 3, however 1 of the iPad minis now shuts off at random times. Pressing the power button does not help. I must Power cycle the device by pressing the power+home buttons. It could stay on for hours with out an issue then all of a sudden.. black. Nothing.

I would really appreciate it if anybody can give me some help on this. Thanks in advance!!