While [ ... ] constructs an array, it returns a reference to the array, not the array itself. That means that $s->{aa}->{'1'} (for example) is a reference to an array. You need to dereference it.

my @a = (
   @{$s->{aa}->{'1'}},
   @{$s->{bb}->{'1'}},
   @{$s->{cc}->{'1'}},
);
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or (minimal change)

my @a = map { @$_ } (
   $s->{aa}->{'1'},
   $s->{bb}->{'1'},
   $s->{cc}->{'1'},
);
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or

my @a = map { @{$s->{$_}->{'1'}} } keys %$s;
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