Did the digitizer you purchased have the Home button included or did you have to transfer the home button from your cracked digitizer?
If the replacement screen came with the Home Button installed, then this is a quality issue and you should take it up with iFixit Support. If the replacement screen did not have the HB pre-installed, then you need to clean off the old adhesive from the previous HB bracket and apply fresh, strong adhesive to insure it holds the button in place tightly.
You can order an extra one of these and cut out what you need or order a kit from Bowler Tech that includes the tape cutouts for the HB bracket.
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