排序可选表单后无法检索信息

I am generating a form with this:

<form class="form-horizontal" role="form" method="POST" id="priority" action="{{ url('/somewhere') }}">
    {{csrf_field()}}
    @foreach($items as $item)
        <li class="list-group-item active">
            {{$item->name}}
            <input type="hidden" name="priority[]" value="{{$item->id}}">
        </li>
    @endforeach
</form>
<button form="priority" type="submit">Save</button>

I made this list selectable using jQuery sortable lists but after changing the position of the options the priority[] does not exist. When I check the form after changing positions, the inputs and the list elements change as intended. Also if I submit the list without chaning anything at all, the priority[] array is actually filled.

Any ideas?