Why are your requirements changing all the time? Maybe you want this:

if ( exists $new->{$TAP}->{$check_field} and 
      (not exists  $old->{$TAP}->{$check_field} or $new->{$TAP}->{$che
+ck_field} ne $old->{$TAP}->{$check_field}) ) {
            $hasUpdated = 1;
            last;
}
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