Docker Collabora: The TLS connection was non-properly terminated

In an attempt to identify the underlying issue with reverse proxy, I’ve remote into my server that hosts Collabora server, pulled the image, run the container and trying to get a proper response directly from the container and exclude the reverse proxy for now. I also, for testing purposes, run another simple container just to demonstrate that Docker is running something at least.

$ sudo docker pull collabora/code
Using default tag: latest
latest: Pulling from collabora/code
Digest: sha256:2f5bad8918259...2003a6e0a475430
Status: Image is up to date for collabora/code:latest

$ docker run -t -d -p 127.0.0.1:9980:9980 -e 'domain=nextcloud\\.mydomain\\.com' --restart always --cap-add MKNOD collabora/code
be484fbc600437e23e3a876eddc52d27b8600e811b3b99579d07be248c0210d4

$ docker ps -a
CONTAINER ID        IMAGE                  COMMAND                   CREATED             STATUS              PORTS                      NAMES
be484fbc6004        collabora/code         "/bin/sh -c 'bash st…"    8 seconds ago       Up 7 seconds        127.0.0.1:9980->9980/tcp   festive_hypatia
79bbe8aadc69        crccheck/hello-world   "/bin/sh -c 'trap \"e…"   About an hour ago   Up About an hour    0.0.0.0:32768->8000/tcp    web-test

$ curl https://127.0.0.1:9980/hosting/discovery -v
*   Trying 127.0.0.1...
* Connected to 127.0.0.1 (127.0.0.1) port 9980 (#0)
* found 148 certificates in /etc/ssl/certs/ca-certificates.crt
* found 599 certificates in /etc/ssl/certs
* ALPN, offering http/1.1
* gnutls_handshake() failed: The TLS connection was non-properly terminated.
* Closing connection 0
curl: (35) gnutls_handshake() failed: The TLS connection was non-properly terminated.

$ curl http://0.0.0.0:32768
<xmp>
Hello World


                                       ##         .
                                 ## ## ##        ==
                              ## ## ## ## ##    ===
                           /""""""""""""""""\___/ ===
                      ~~~ {~~ ~~~~ ~~~ ~~~~ ~~ ~ /  ===- ~~~
                           \______ o          _,/
                            \      \       _,'
                             `'--.._\..--''
</xmp>

$ curl https://0.0.0.0:32768
curl: (35) gnutls_handshake() failed: An unexpected TLS packet was received.

The last two are the simple containers just for testing. The last one was just to see that a different message was shown when I know for sure SSL is not available.

How do I debug the collabora/code container? Can I, for example, SSH into this container? Is it an issue with it’s SSL keys? I didn’t set these up and assuming that this is part of the image(?)