rasa: Web chat unresponsive; API fine, other channels fine

Rasa version: 1.3.2 Rasa X version: 0.21.0 Operating system: OSX. Tested in Chrome, Safari, and Firefox; same result.

Issue: “Talk to your bot” doesn’t respond to anything; not even “Restart”. Just a pulsing ellipsis appears. (“Interactive Learning” works just fine, but it uses different API calls). The API seems to be returning a result, but that result doesn’t render to webchat. See short screencast to see the problem in action: https://www.dropbox.com/s/6ofz8gyn558gurk/screen recording 2019-09-17 at 4.34.54 pm.mov?dl=0

Error: There are no errors in the Chrome developers’ console.

Content of configuration file (config.yml) (if relevant):

pipeline: supervised_embeddings
language: en
policies:
- name: MemoizationPolicy
- name: KerasPolicy
- name: MappingPolicy

Content of domain file (domain.yml) (if relevant):

intents:
  - greeting
  - insurance-car
  - insurance-home
  - insurance-business
templates:
  utter_greeting:
    - text: Hi there!
  utter_insurance-type:
    - text: What kind of insruance do you need?
  utter_start-car:
    - text: What kind of car?
  utter_start-business:
    - text: Is your business incorporated?
  utter_start-home:
    - text: What year was your house built?
  utter_start_car2:
    - text: 'Ooh, nice car!'
actions:
  - utter_insurance-type
  - utter_greeting
  - utter_start-car
  - utter_start-business
  - utter_start-home
  - utter_start_car2