iPhone 6 touchpad problem.

iPhone 6 touchpad problem it works for 4 to 5 days properly. After that it miss work, it doesn’t work properly & stop working. Again when I remove it from connector & fix it, it again work properly for 4 to 5 or even for more days. Same happens from last one month. I have changed it with other original working display but same here. What should be the problem? Phone untouched.
Can anyone help?
Thank you in advance.