Can send HTTP requests from one NodeJS Docker container on Laptop to other NodeJS Docker container on Raspberry Pi, but not vice versa

Question

I have a robot where I am running a NodeJS server under Docker Compose v2. On my laptop I am running another NodeJS server under Docker Compose. Both containers are setup more or less the same. Here is the docker-compose.yaml:

version: "3.9"

services:

  server:
    build: ./
    command: npm run dev:start
    volumes:
      - ./:/usr/app
      - /usr/app/node_modules
    network_mode: host
    ports:
      - "${PORT}:${PORT}"
    depends_on:
      - db

  db:
    image: mariadb:10.6
    volumes:
      - db_data:/var/lib/mysql
      - ./db_init/:/docker-entrypoint-initdb.d/
    environment:
      MARIADB_RANDOM_ROOT_PASSWORD: yes
      DB_ADMIN_PASSWORD: ${DB_ADMIN_PWD}
      DB_APP_PASSWORD: ${DB_PWD}
    ports:
      - "${DB_PORT}:3306"

volumes:
  db_data:

Network is managed by DHCP on the robot:

• Laptop: 192.168.11.200, NodeJS port 8100
• Robot: 192.168.11.110, NodeJS port 8000

I can send HTTP requests from the laptop to the robot (both are running Ubuntu). But not in the other direction, neither does work CURL. I can ping both machines from both each other. It did work via Ethernet the week before, that I used to setup manually. So I'm quite stupified why it doesn't work with WiFi anymore.

I also have a Docker container with a frontend running on the laptop. It can reach the backend.

Any idea what the issue could be? Is that a problem with the network or Docker setup?