Touchscreen randomly not functioning after unlocking?

I replaced my iPhone screen today, however I am having some issues with the touchscreen.

When I am using the phone, the screen stays responsive and runs with no issues. However, if I lock my phone and wait for 20 seconds or so, the touchscreen will indefinitely not work upon unlocking the device-despite the actual LCD still functioning perfectly.

However, if I lock and then unlock my phone again immediately after this, the touchscreen will work perfectly without any issues; until I leave the phone locked for another 20 seconds etc...

So far I have reconnected all the flex cables between my new screen and the phone twice (no difference seems to be made) and I have done a hard/soft restart and a reset of my phone.

I hope that anyone could shed any light on this being either a software or hardware issue; as although it seems to be software related, this problem only occured after replacing the screen. No movement of the phone is needed for the touch screen to work/stop working, which just generally confuses me!

Thanks very much in advance for any answers! (:

(Sorry about my avatar... linked to my gaming accounts!)