If all that is needed is a count of how many characters are the same, this can be reduced to:

#!/usr/bin/perl

use strict; # https://www.perlmonks.org/?node_id=11155923
use warnings;

my $str1='LFGSLSIIVAHHM';
my $str2='LFGSLSIIVSHHM';

use Algorithm::Diff qw(traverse_sequences);
my $same = 0;
traverse_sequences( [ split //, $str1 ], [ split //, $str2 ], {
  MATCH => sub { $same++ },
  } );
print "$same characters are the same\n";
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which outputs:

12 characters are the same
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