It is most likely a faulty part and has dead spots with the touch in the Digitizer. It's either the part or it is not plugged in all the way. I would take it back where you got the repair done to see if they can figure out if it's the part and double check their work, but parts can be bad from the vendor , it's a problem that techs often overlook , or if they didn't double check after putting the part on may have not noticed these dead spots. you usually have anywhere from 30-90 days at most repair shops to have it warrantied so i'd take it back asap.