The error likely is on this line:

open(SUMMARY, ">:utf8", ">Item Summary.txt");
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and Perl would have told you about it, had you used proper error checking:

my $outfile = ">Item Summary.txt";
open(SUMMARY, ">:utf8", $outfile)
    or die "Couldn't create '$outfile': $!";
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Of course, the warning that SUMMARY is a closed filehandle is still true, but not because it was closed behind your back but because it was never opened. Also, XML::Twig does not play into the problem at all, neither does UTF-8.