Interface not instantiable while building class (Model observer)

Hi,

I'm using a Model observer to create related entries on the Model's `created` event. I'm using this repository package to communicate with my database. I bind the RepositoryInterfaces to their concrete classes in my `RepositoryServiceProvider`, which I added to the `'providers'` array in my `config/app.php`. When my Observer runs, however, I get the following error:

```
Target [App\Repositories\Interfaces\ExamAttemptQuestionRepositoryInterface] is not instantiable while building [App\Observers\ExamAttemptObserver].
```
I've created a little test interface `MyInterface`, implemented it in `MyClass` and bound the interface to the implementation in my `RepositoryServiceProvider`, just like I did with all my other repositories. The observer doesn't throw an exception when I resolve `MyInterface` in the constructor.
```
interface MyInterface
{
public function test(): string;
}
```

I've raised an issue on [Laracasts](https://laracasts.com/discuss/channels/laravel/interface-not-instantiable-in-model-observer), but was hoping to also get help from here, since I'm unsure if where the issue originates.

Kinds regards,