WebDav in docker container - failing?

I’m currently running the latest docker container and testing out a Wordpress plugin that uses WebDav.

Running the plugin against the demo v12 web site (https://demo12.nextcloud.bayton.org) works fine
Running the plugin against the Docker container fails, but unfortunately I can’t figure out why.

Both versions are 12.0.0 - can anyone help point me to why the one works but not the other?

*Update: I meant to say, all other functions seem to be working fine in the live site

Just for extra info here, the plugin developer has confirmed that the it uses streaming support for uploading partial file requests. Is there something in the Docker image that is missing perhaps, e.g. a library needs installing for this?