Why does it keep logging out (has over 50% battery charge)

Hi all,

I recently changed the battery on my iphone 6s using the ifixit kit, followed the instructions. The only thing I didn't do was remove the screen entirely, had it propped up at 90 degree angle while I replaced the battery. I also found that the battery connector wasn't so flat, I pressed it down and screwed it in.

The first 2 days it was fine but today after a full charge it logs me out when I'm on it for a about 1min. Then I need to log in again either password or touch id and it goes to home screen not to what I was doing before. For example I'm on the internet then then loading wheel appears, goes black and then then the log in screen appears, then I'm back to homescreen.

Help? What might be wrong?