New Install, "Failed to establish socket connection ..."

[sbw]

I followed the Docker Compose instructions. Logged in as admin. I can edit a text file and a Markdown file.

I created a new OpenDocument. Immediately a pop-up appeared, apparently from Collabora:

Failed to establish socket connection or socket connection closed unexpectedly. The reverse proxy might be misconfigured, please contact the administrator. For more info on proxy configuration please checkout https://sdk.collaboraonline.com/docs/installation/Proxy_settings.html

I don't know what "the reverse proxy" refers to, or how to troubleshoot it.

Maybe unrelated, but 'docker logs (collabora ID)` says:

wsd-00001-00025 2025-12-07 22:13:07.527823 +0000 [ websrv_poll ] WRN #-1: SSL verification warning: 'self-signed certificate' seen on CheckFileInfo for [https%3A%2F%2Fwopiserver.(hostname elided)%3A443%2Fwopi%2Ffiles%2F580a5d17a7c9f18e5cf543d54a3c35a02aaaa6ce4a42586e5571d7dc90e8cd46]| wsd/RequestVettingStation.cpp:381

I didn't see anything relevant in Common Issues & Help. I believe the Accept Self-Signed Certificates section is referring only to the Lets Encrypt staging certificates used during the installation. I've already done the Apply a Real SSL Certificate step, so my web server no longer warns about the certificate.

Thanks for any troubleshooting guidance you can give me!

[sbw]

Sorry, I forgot to say I used production release container 4:

OC_DOCKER_TAG=4

[micbar]

This is an issue with the latest patch release of traefik. There has been a breaking change.

see opencloud-eu/opencloud-compose#173 for possible solutions.

[sbw]

Thanks very much. I might just change my .env to OC_DOCKER_TAG=3 for now.

(Sorry, I tried to search the issues before starting this thread. Not sure why I didn't find it.)