Vertical and horizontal stripes after screen replacement, why?

I had my iPhone 7 repaired yesterday. The screen was replaced because I broke it. It was working fine up until today, every so often green and black vertical lines appear then the screen turns into as it was set to "inverted colours" and then slowly turns into a white screen. Locking and unlocking the screen instantly fixes ( which is why i think that it might be something with the software) the problem but it is quite annoying as it happens every 2 minutes. I tried soft reset but it didn't solve the problem. I will obviously bring it back asap, but I would like to have and idea of what the problem could be ?