php - 尝试从CSV下载URL，它随机URL停止

Question

I've tried searching for this issue but couldn't find out why it is actually failing at random stages.

I have a CSV with 2 columns, ID and URL, there are 100 rows. I have the following code to loop through the CSV rows and use put_file_contents() to download the data at the URLs into files that are named [ID].jpg.

I am also outputting data to the screen each time around the loop and adding a line to "log.txt". For some reason it just stops working after a random URL and doesn't put anything in the error_log.

Sometimes it's after 17 URLs, sometimes it after 27, sometimes its after 49. I am at a loss as to why it fails.

<?php

set_time_limit(3600);

$data = array_map('str_getcsv', file('IDtoImageURL2.csv'));

$total = 0;

echo "Count total: ".count($data)."<br /><br />";

for($i = 1; $i < count($data); $i++)
{
    file_put_contents("log.txt", $data[$i][1]." - ", FILE_APPEND | LOCK_EX);
    $total++;

    $url = $data[$i][1];
    $img = "photos/".$data[$i][0].'.jpg';
    $img2 = "photos/named/".$data[$i][0].'.jpg';

    echo "<b>Getting ".$data[$i][0].":</b><br />";
    echo "URL: ".$data[$i][1]."<br />";
    echo "putting $img<br />";
    echo "putting $img2<br />";

    $imgData = file_get_contents($url);

    if($imgData)
    {
        file_put_contents($img, $imgData);
        file_put_contents($img2, $imgData);

        echo "<b>Done</b><br /><br />";

        file_put_contents("log.txt", "done".PHP_EOL, FILE_APPEND | LOCK_EX);
    }
    else
    {
        echo "<b>Failed</b><br /><br />";

        file_put_contents("log.txt", "failed".PHP_EOL, FILE_APPEND | LOCK_EX);
    }   
}

echo "Total: ".$total;

?>

Here is the CSV data that I'm working with.

What's strange is that sometimes it posts some of the echo output to the screen and sometimes it just silently errors with a blank scree. The URLs are looped through in the same order and so I don't understand why the results keep differing. Any input would be greatly appreciated.

Thank you for your time