Loading animation and attempt to POST to localhost:3000

Hi all,
I'm running Haproxy (ssl offload) ->rocketchat(docker).
The container starts ok but in the browser i can only see the three dots animation and in my browser dev-tools/network i see a failed POST request to localhost:3000.

The request is:

http://localhost:3000/__meteor__/dynamic-import/fetch

I would expect that the configuration of the url is picked up from .env ROOT_URL
It seems to me that something keeps using localhost:3000 for URL building.
Do you guys know what this can be?

Here is my env, the compose.yaml is untouched:

### Rocket.Chat configuration

# Rocket.Chat version
# see:- https://github.com/RocketChat/Rocket.Chat/releases
#RELEASE=
# MongoDB endpoint (include ?replicaSet= parameter)
#MONGO_URL=
# MongoDB endpoint to the local database
#MONGO_OPLOG_URL=
# IP to bind the process to
#BIND_IP=
# URL used to access your Rocket.Chat instance
ROOT_URL=https://rchat.example.com
# Port Rocket.Chat runs on (in-container)
#PORT=
# Port on the host to bind to
#HOST_PORT=

### MongoDB configuration
# MongoDB version/image tag
#MONGODB_VERSION=
# See:- https://hub.docker.com/r/bitnami/mongodb

### Traefik config (if enabled)
# Traefik version/image tag
#TRAEFIK_RELEASE=
# Domain for https (change ROOT_URL & BIND_IP accordingly)
DOMAIN=rchat.example.com
# Email for certificate notifications
#LETSENCRYPT_EMAIL=

Do I need to disable traefik in compose.yaml?

Many thanks in advance.

Start with the untouched compose.yaml and the .env values, especially ROOT_URL, then reproduce the browser request to /meteor/dynamic-import/fetch through the HAProxy SSL-offload setup. Done means the deployed Rocket.Chat instance loads without attempting to POST to localhost:3000.