我认为这是设计有缺陷的征兆。看来你在找3个球员的分数。您在3行上循环，但尝试访问每个迭代中所有3个玩家的数据。相反，您应该在每个玩家各自的迭代中访问他们的数据，并建立一个玩家数据列表。
为了直接回答您的问题，在迭代1中，您尝试访问元素0、1和2，但是 $rows 只填充了0。

+-----------+-------------------------+--------------------------+
| Iteration | You're trying to access | You only have access to  |
+-----------+-------------------------+--------------------------+
|         1 |                   0,1,2 |                        0 |
|         2 |                   0,1,2 |                      0,1 |
|         3 |                   0,1,2 |                    0,1,2 |
+-----------+-------------------------+--------------------------+

例子

<?php
// Turn on error reporting
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

// Show MySQL errors as PHP exceptions
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

include '../connect_database.php'; 

// Build up this list inside the loop. 
$scores = [];

$sql = "SELECT score FROM dailyscore Where Id IN (1,2,3)";
date_default_timezone_set('America/New_York');
$result = $connect->query($sql);
while ($row = mysqli_fetch_assoc($result)){
    // You only have access to a single $row here. 
    // Build up an array of the data you want instead of tring to access "other rows"
    $scores[] = $row['score'];
}

// Now, you can use $scores to build $list... or build $list inside the loop. 
?>

编辑
你介意给我举个例子说明如何将数组结果分配给这样的对象吗$list['scores']=array（'data'=>$id1，'data1'=>$id2，'data2'=>$id3）；

<?php
// Turn on error reporting
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

// Show MySQL errors as PHP exceptions
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

include '../connect_database.php'; 

// Build up this list inside the loop. 
$scores = [];
$counter = 0;

$sql = "SELECT score FROM dailyscore Where Id IN (1,2,3)";
date_default_timezone_set('America/New_York');
$result = $connect->query($sql);
while ($row = mysqli_fetch_assoc($result)){

    $keyName = 'data';

    if ($counter > 0) {
        $keyName = 'data' . $counter;
    }

    $scores[$keyName] = $row['score'];

    $counter++;
}

$list['scores'] = $scores;

echo json_encode($list);