As pretty much everyone else has said now the problem is in your data - the stuff you are not showing us. See How to ask better questions using Test::More and sample data for rationale and instructions to produce an SSCCE like this one.

use strict;
use warnings;

use Test::More tests => 1;
use Test::NoWarnings;

my $line = 'foo=a,bar=3,baz=Fizzlegrapplebaum';
my @data = split(',', $line);
foreach my $datapair (@data) {
    my ($label, $data) = split('=', $datapair);
    my $out = "label: $label; data: $data\n";
}
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Of course, here the test succeeds because the initial data is good. Your task is to make this test (or one very similar to it) fail by supplying the duff value for $line.