Untested, simplified code suggestion:

sub get_lower_level_ehms_count
{
        my %design_hash   = %{$_[0]};
        my %ehm_count ;
        my $embedded = $design_hash{'EMBEDDED_HMS'} or return \%ehm_co
+unt;
        for my $emb (@$embedded)
        {
             my $design_top = $emb->{'TOP'};
                        
             if($emb->{'EMBEDDED_HMS'})
             {
                    $lower_levels = get_lower_level_ehms_count($emb); 
                    $ehm_count{$_} += $lower_levels->{$_} for keys %$l
+ower_levels;
             }
             $ehm_count{$design_top} += scalar @{$emb->{'INSTANCES'}};
 
        }

        return \%ehm_count;
}
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