Your problem is that $fn isn't a lexical variable --- you'll want to use my() so the anonymous subroutine acts as a closure around each lexical $fn. See the difference between these two snippets:

my @subs;
foreach $fn (1,2) {
    push @subs, sub{print "$fn\n"};
}
$fn = 42;
foreach $sub (@subs) {
    $sub->();
}

@subs = ();
foreach my $fn (1,2) {
    push @subs, sub{print "$fn\n"};
}
$fn = 42;
foreach $sub (@subs) {
    $sub->();
}
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