Your script appears to be working correctly for me. Try this test program

#!/usr/bin/perl
use strict;
use warnings;
use Text::Wrap;
use Text::CSV_XS;

my $csv = Text::CSV_XS->new (
 { binary => 1, eol => "\r\n", auto_diag => 1 });
open my $fh, ">", "wraptest.csv" or die "$!";

my @data = (
  ['1a this is more than 20 characters',
   '',
   '1c and another one that is more than 20 characters'],
  ['2a this is more than 20 characters',
   '',
   '2c and another one that is more than 20 characters'], 
);

for my $row_index (0..1){
  my @row;
  for my $col_index (0..2){
    my $source_cell = $data[$row_index][$col_index];
    my $value;
    if ($source_cell){
      local $Text::Wrap::columns = 20;
      $value = wrap ("", "", $source_cell);
    }   
    push @row , $value;
  }
  $csv->print ($fh, \@row);
}
close $fh;
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