On on-premise deployment if API is configured to use custom policy, its Policy chain is displayed empty after removal of custom policy from apicast.
Steps to reproduce:

• create custom apicast image with custom policy & deploy
• create/modify an API to use that custom policy
• change/revert apicast deployment back to image without custom policy.
  Checking the API in admin web interface, policy chain in Integrations / Configuration / Policies is now empty.
  Workaround: Remove custom policy from policy chain before removal from image.