Avatar upload not working when using flysystem AwsS3Filesystem as filesystemComponent

[iadj]

In my yii2-starter-kit installation, I configured the fileStorage module to use creocoder\flysystem\AwsS3Filesystem (which now has a pull request that supports S3 v3) as filesystemComponent.

I haven't touched any code except for common/config/base.php, setting a awss3Fsmodule:

    'awss3Fs' => [
       'class' => 'creocoder\flysystem\AwsS3Filesystem',
       'key' => getenv('S3_KEY'),
       'secret' => getenv('S3_SECRET'),
       'bucket' => getenv('S3_BUCKET'),
       'region' => 'us-east-1',
     ],

and fileStorage module:

    'fileStorage' => [
        'class' => '\trntv\filekit\Storage',
        'filesystemComponent'=> 'awss3Fs',

        'as log' => [
            'class' => 'common\behaviors\FileStorageLogBehavior',
            'component' => 'fileStorage'
        ]
    ],

When I try to upload an avatar using the standard avatar-upload action in modules/user/controllers/DefaultController.php, I get the following error:
exception 'yii\base\ErrorException' with message 'fstat() expects parameter 1 to be resource, integer given' in vendor\league\flysystem\src\Util.php:256

How can I fix this issue?