Event cards are blank

[T]

I have set up a simple project and am pulling data from Google Calendar and passing it to Kalendar.

Kalendar creates event cards in the right places on the calendar but they are all blank. See attached image.

<template>
  <Kalendar :configuration="calendar_settings" :events="events" />
</template>

<script>
import Vue from 'vue';
import PortalVue from 'portal-vue';
import {Kalendar} from 'kalendar-vue';
Vue.use(PortalVue);

export default {
  name: 'Calendar',
  components: {
    Kalendar,
  },
  data: () => ({
    calendar_settings: {
      day_starts_at: 7,
      cell_height: 10,
      scrollToNow: true,
      read_only: false,
      past_event_creation: false
    },
   events: [
          {
      summary: 'B in M 🎤',
      start: { dateTime: '2020-03-18T18:00:00Z', timeZone: 'Europe/Dublin' },
      end: { dateTime: '2020-03-18T19:00:00Z', timeZone: 'Europe/Dublin' },
    },
    {
      summary: 'O & F 🎤',
      start: { dateTime: '2020-03-18T19:00:00Z', timeZone: 'Europe/Dublin' },
      end: { dateTime: '2020-03-18T21:00:00Z', timeZone: 'Europe/Dublin' },
    },
    ...  // many more
     ]
  }),