Update `index` property in a collection of given IDs - laravel

Question

Using a POST on my front-end (React.js, with react-beautiful-dnd), I'm trying to update the position of the items a user has stored.
My strategy is to send over an updated index of IDs that are ordered in the specified position.
My Data (example, simplified)
┌────┬────────┬───────┐
│ id │ title │ index │ <── my "position"
├────┼────────┼───────┤
│ 1 │ Apple │ 4 │
│ 2 │ Banana │ 1 │
│ 3 │ Mango │ 3 │
│ 4 │ Kiwi │ 2 │
│ 5 │ Orange │ 0 │
└────┴────────┴───────┘
New positions array (anatomy)
$value: sorted ids ------> [3, 2, 5, 1, 4]
: : : : :
$key: new index will be… 0, 1, 2, 3, 4
The Code
The controller ingests an array that derives the new positions from the keys of the array. It loops then through the collection of given IDs and reassigns them the updated index.
public function reorder(Request $request) {
$newIndex = $request->newIndex;
$items = Item::whereIn('id', $newIndex)->get();
foreach ($newIndex as $key => $value) {
// TODO: check if $item->index needs to be rewritten at all
$item = $items->find($value);
$item->index = $key;
$item->save();
}
return response('Success', 200);
}
dd() of $request->input
array:1 [
"newIndex" => array:5 [
0 => 4
1 => 1
2 => 2
3 => 5
4 => 3
]
]
The problem
It seems… the code only works once? Did I miss something? The POST fires every time and the set array is accurate, so the issue is not on the frontend side of things.