Cannot trigger automation based on calendar event

Configuration
2

One possible cause is the update window. During normal operation, the listener for Calendar event triggers only updates every 15 minutes.

When testing, you need to account for this by setting the event’s start to at least 15 minutes in the future, or by forcing the listener to update by reloading the calendar and automation after you have created the test event.

Calendar - Automation (bottom of the section)

FWIW, I call the following script whenever I have an automation that creates calendar events that might fall into the 15 minute window:

Calendar/Automation Reload Script 
alias: Reload Calendar & Automation
fields:
  calendars:
    name: Calendars
    description: ""
    required: true
    selector:
      entity:
        multiple: true
        filter:
          domain: calendar
  automations:
    name: Automations
    description: ""
    required: true
    selector:
      entity:
        multiple: true
        filter:
          domain: automation
sequence:
  - action: homeassistant.update_entity
    metadata: {}
    data:
      entity_id: "{{ calendars + automations }}"
  - repeat:
      for_each: "{{ calendars}}"
      sequence:
        - action: homeassistant.reload_config_entry
          metadata: {}
          data: {}
          target:
            entity_id: "{{ repeat.item }}"
  - action: homeassistant.update_entity
    metadata: {}
    data:
      entity_id: "{{ calendars + automations }}"
description: ""
icon: mdi:calendar-question-outline