I did realise that the docker host was not resolving DNS properly (for some reason, its resolv.conf comes back to 127.0.0.1, I was manually changing it to 8.8.8.8 to get it working), and I didn’t want to spend time on it as I was moving to another host/datacenter:
When DNS is failing, docker containers are not updated.
If you try a new build, it should work.
When I couldn’t get the new host, I forgot to at least fix DNS on the old host.