The answer isn’t sticking out to me, but make sure that:
- Both NC and Collabora are able to resolve each other’s names
- Both are pointing to the reverse proxy even when talking to each other
- The reverse proxy is presenting a valid certificate for both
Here is another example I wrote myself that you can cross-reference.
https://help.nextcloud.com/t/howto-ubuntu-docker-nextcloud-talk-collabora/76430