Why is my new screen unresponsive?

Ok this is quite obscure and is definitely racking my brain. 

I have a XR that I wanted to replace the screen on. I bought a donor phone that has a good condition original screen. When testing this donor screen on the phone it came on it works well and touch responsiveness is perfect. 

However, after transferring this screen to the phone I want to fix the entire top half of the screen is completely unresponsive to touch. I reseated the connection multiple times but always the same issue.

When I transfer the screen back to the donor phone it works perfectly again.

This made me believe it might be an issue with the phone I want to fix and so I put the original cracked screen back on but the response on it is completely normal again.

Therefore I am completely puzzled as to what is causing this. It’s like two working things come together to make a broken thing.