iPhone 7 PLUS is restarting after screen replacement

Hi there!

So i have the following problem.

I just finished an iPhone 7 Plus. Replaced it with an OEM screen, also had to replace the front cam flex because of the famous ' no speaker' problem. (Before the repair i made sure the battery was disconnected!) Phone had no waterdamage, just the usual screencrack.

After replacement everything is working fine (touch id, speaker, front cam and screen)

But somehow when i enter the phone and open Facebook for instance, it shuts down and i have to restart it. Also when opening other apps, it will randomly shut down.

Any idea what is causing this?

Many thanks!