Power Button Turns On Device But Doesnt Work Otherwise

Working on an iPhone 5s which required screen replacement.

Screen replaced ok and device powered back on touch, display all fine.

However although the power button boots the device it then becomes non functional.

It wont lock device or will it power off device if held, it still somehow turns device on.

I placed board into another housing as the screen damage was up at corner beside power button. Results are the same, boots device but doesn't work for other functions.

Thought this very odd, has anyone seen it before?

Thanks in advance!!