$a->[ 1.. 4 ] is not valid array slice syntax. You need an @ in there for it to be so:

[0] Perl> $a = [ qw(mary had a little lamb with mint jelly) ];;
[0] Perl> $b = [ @{ $a }[ 1 .. 4 ] ];;
[0] Perl> print @$b;;
had a little lamb
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I'm surprised that you didn't get a warning or two along the lines of:

Using an array as a reference is deprecated at ...
Argument "" isn't numeric in array element at ...
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