Text::CSV_XS versions before 1.65 for Perl allow record splitting by writing strings used as numbers without quotes in combine.
combine and print do not check whether a field needs quotes when its value has Perl's integer or numeric flag set. Perl sets these flags on a string used in a numeric operation when it parses as a number, which allows leading and trailing whitespace. With binary set, as csv does by default, "12\n" passes a check such as $qty > 0 and is then written unquoted with its newline.
A value validated as a number can end the record early and turn the fields after it into a separate row.
Upgrade to Text-CSV_XS 1.65 or later.