This was an extremely frustrating one. I had a local prefect running and had this one running from this docker compose config:

prefect-server:
    image: prefect_custom
    build: .
    command: prefect orion start
    depends_on:
      postgres:
        condition: service_healthy
      minio:
        condition: service_healthy
    healthcheck:
      test: curl --fail localhost:4200/api || exit 1
      interval: 5s
      timeout: 5s
      retries: 3
    ports:
      - 4200:4200
    environment:
      PREFECT_ORION_API_HOST: 0.0.0.0
      PREFECT_ORION_DATABASE_CONNECTION_URL: <postgresql+asyncpg://prefect>:test-password@postgres:5432/prefect_server
      PREFECT_ORION_ANALYTICS_ENABLED: "false"
      PREFECT_API_URL: <http://localhost:4200/api> # Client (browser) will query this API when accessing Prefect UI
      PREFECT_LOGGING_SERVER_LEVEL: INFO
    volumes:
      - ./volumes/prefect/data:/root/.prefect
      - ./volumes/prefect/flows:/flows
    networks:
      - prefect

When I accessed the UI it was fetching stuff from the local prefect because of

PREFECT_API_URL

. Switching it to the host of the machine solved it:

REFECT_API_URL: http://<host>:4200/api