I blame your uninformative error message:

    # Lookup domain with whois
    $who = whois($d) or die "Cannot reach whois server";

    # Get expiration date
    if ($who =~ m/expir.*?(\d{2}-\w{3}-\d{4})/i) {
        $edate = $1;

    }elsif ($who =~ m|renewal-date.*?(\d{4}/\d{2}/\d{2})|i) {
        $edate = $1;

    }else{
        $expires{$d} = "Whois failed";
        next;
    }
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Once you replace your "Whois failed" with something more informative, it should become much clearer where the error lies:

        $expires{$d} = "Whois failed for $d: Couldn't decipher '$who'"
+;
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