in your code, you put it into @row, which is wrong, a ref is a scalar:

my @column_names = @{$_read_sth->{NAME_lc});
local $\ = "\n";
#         v---- not a @
while (my $row = $_read_sth->fetchall_arrayref) {
    print join ",", @$row; # Extremely oversimplified
    }
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returning fetch (or fetchrow_arrayref) into @row will cause a structure like this:

$VAR1 = [
          undef
        ];
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which is a true value, causing the endless loop