Phone crashes often after display replacement.

A friend of mine had a cracked display on her galaxy A5 2017. She was on holidays and got it fixed there in a repair shop. But now the phone started to crash randomly. It goes like this:

• Turn phone on
• unlock sim and phone —> display works fine
• lock phone —> screen turns off (as it should)
• press home or lock button to unlock again —> two possible outcomes:
  1. display turns on, ready to unlock, everything works fine
  2. phone crashes, flashes some orange lines across screen and flashes the soft buttons (the ones left and right of the home button) and restarts

I have already opened the phone up but could not see anything wrong. We also noticed that the blue light filter does not work anymore with the new display.

What can I do to try and fix it? Should i just buy a new display or will that not work?