Hi,
The touchscreen is on a different cable as the OLED. So a rip in the touch cable could be what's causing this. Otherwise the screen may be faulty. Have you filed a return with iFixit yet? if you can prove that no cable got ripped during the repair they might send you a replacement screen.[br]
https://ifixit-eu-en.helpscoutdocs.com/category/269-contact-us[br]
You can always try to clean the cable contacts and reseat the cables, a piece of dust inside the connector could also be the cause.