Cannot insert/edit pictures in documents

I have successful installed the Docker image on a VM with nextcloud. Ic can create and edit documents with collabora but I am not able to insert or edit pictures in my documents.
The only Information I have in my log is:
Debug | no app in context | Loaded WOPI Token record: {"id":"11","owner_uid":"USER","editor_uid":"USER","fileid":"198","version":"0","canwrite":"1","server_host":"https://sub.DOMAIN.TLD/","token":"alT9vqFuRDFte15l5cTOz6tJa2isAS0h","expiry":"1506586094"}.

Can anyone give me a hind, where I have to search for a solution?

We have exactly the same problem. Does someone have an answer to this?
Thank you!