MinIO - strange naming and it gets more and more full

Nextcloud version: 23 (Docker)
Operating system and version: Ubuntu 20.04

Hi community,

I have setup nextcloud with an external primary storage via minio.
In nextcloud everything works fine but my minio bucket looks strange to me.
I only get file names like urn:oid:1004 and my buckets becomes more and more full without storing more files in my nextcloud.

My config.php section for minio looks like this:

 'objectstore' => 
  array (
    'class' => 'OC\\Files\\ObjectStore\\S3',
    'arguments' => 
    array (
      'bucket' => 'nextcloud',
      'autocreate' => false,
      'key' => 'SecretKey',
      'secret' => 'SuperSecretKey',
      'hostname' => 'minio',
      'port' => 9000,
      'use_ssl' => false,
      'use_path_style' => true,

Did anybody experienced a similar behavior while using minio as an primary storage?