tldr: I recommend you change the Vehicle IP address to 127.0.0.1.
I think the issue is a poor interaction between the “Vehicle IP address” and BlueOS networking setup. While BlueOS is reachable from outside via the blueos-avahi.local domain name, it’s not reachable from within BlueOS at that domain name.
Confusingly (even to me), the Sonarlink and Discovery Options Server field is resolved from your browser, whereas the “Vehicle IP address” field is resolved from within the docker container.
From outside blueos (on a linux computer or on the Raspberry Pi outside docker), you can list all hosts advertising their address (install with sudo apt install avahi-utils).
$ avahi-browse -at
Trying this from inside blueos shows that it can’t reach the avahi daemon:
$ docker exec -it blueos-core bash
Failed to create client object: Daemon not running