Failed to load documents after update from 14.0.3 to 15.0.12

Hello,
after updating our Nextcloud from version 14.0.3 to 15.0.12, our collabora integration stopped working. Whenever I am trying to open a document I get the message that the document could not be loaded from disk.

We are using CODE + nginx as docker-containers. This is the Log output when trying to access a document:
https://gist.githubusercontent.com/ibot3/4a3844c751e9f5250ac74cc8c3ef212f/raw/5194da68e7fba7a30e6aca263f5c17f21fced8ea/gistfile1.txt

This is our nginx config: https://gist.github.com/ibot3/35c27d09e539e925d8f1cb30495d2446

We are using the newest versions of CODE (4.0.8.2) and nextcloud/richdocuments (3.4.3).

I hope that someone has an idea how to fix this.

Best regards,
Jakob