Touch screen not working after screen replacement

Hi all, I do a lot of work in repairing iPhones for people however i have never had this issue happen. I got given an iPhone 6S Plus to change the screen and battery on, everything worked fine before i started working on it. However after transferring the screen the touch screen wouldn’t work, it isn’t detecting any touch what so ever. Everything else works. I put the old screen back on and that doesn’t work either now. I disconnected the battery before working on it so it couldn’t of being a short and all the connectors and cables are in perfect condition and are not broken. I suspect it could be an issue on the logic board but I am unsure. I have even re-installed the iOS to see if it was software but it doesnt seem to be. Does anyone have any ideas?