There may be leftover adhesive or debris in the device or even a faulty screen. I would carefully open it back up and inspect for debris.
Last month I replaced a screen on a 4A. A week later, the customer came back with a green line, and no signs of physical damage. Upon opening the device, I found a tiny shard of glass, about the size of a grain of salt stuck in the back of the display. It was aligned exactly with the line on the screen.