我在GitHub上的Laravel Framework问题跟踪器上发布了一个类似的问题，作为可能的错误(不确定是否会发生这种现象)，并在那里找到了答案.

I posted a similar question as a possible bug (was not sure whether this behavior was something expected) on Laravel Framework issue tracker on GitHub and found the answer there.

结果是，您无法在全局查询范围构造函数中访问经过身份验证的用户，但可以在apply()方法中对其进行访问.

Turns out, you cannot access the authenticated user in the global query scope constructor, but it is accessible in the apply() method.

所以代替:

public function __construct() {
    $this->region_id = Auth::user()->region_id;
}

public function apply(Builder $builder, Model $model)
{
    $builder->where('region_id', $this->region_id);
}

我必须做:

public function apply(Builder $builder, Model $model)
{
    $region_id = Auth::user()->region_id;

    $builder->where('region_id', $region_id);
}

在GitHub 此处上链接到该问题.

Link to the issue on GitHub here.