$queue[0] contains a reference to a reference to an anonymous array. This will illustrate:

my @queue;
$queue[0] = \[1,2,3,4];

print "$queue[0]\n";
print "${$queue[0]}}\n";
print "@{${$queue[0]}}\n";

my $ref = ${$queue[0]};
print "$ref->[1]\n";
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Gives:

REF(0x3a09c)
ARRAY(0x3a1bc)}
1 2 3 4
2
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Although, judging from the doc for threads::shared you might still have issues.