Ive come across this issue when working on a galaxy s4 phone . What Ive found is that when reassembling the phone the little white pads, that are use for the back button and the menu on either side of the home button, got folded.
Samsung Galaxy Note 4 Display Assembly Replacement
If you look in step 4 of the guide you'll see the white pads,on either side of the home button, if the pad gets folded or if the adhesive paper that surrounds the pad gets over the pad it wont work and it also can affect the touch functionality of the screen. Hope this helps
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