Ionic2-Calendar works in browser, not on device?

I am using Ionic2-Calendar in my app wth Ionic4 and Angular 8. It was working fine, but as I have added new native plugins to my code, (moving on thinking I’d completed the Calendar part :-S) the calendar has stopped initialising properly on the device. (A Samsung A8 with Android 9) which interestingly has recently been updated. My situation is vitually identical to this post on Stack Overflow, with the same error message.

I am suspecting a tiiming and PLATFORM READY type of issue, but in my App.component like most others, starts with:

  ngAfterViewInit() {

  async initializeApp() {
    this.platform.ready().then(async () => {
     .... a chain of initialisations till ..
                  // Now get the appointments out of the store
                  this.userService.getAppointmentsStore().then( (appts) => {
                    console.log('At Startup - Got Appointments from Store');
                    this.userService.appointments = appts;
    .... more initialisations.

the userService.appointments is the 'eventSource for the calendar.

This works fine in the browser using ionic serve. But obviously there are key differences, such as no cordova, not the ame device etc.
I have logged the appointments in the 'ngOnInit function, and they are there. I have also taken out the calendar.loadEvents from the ngOninit and it stll falls over. I still had the event source though and working through trying other things.

Does anyone have any thoughts? Will the code there as written really wait for the device ready or do I need to do it in eg the calendarPage module, or page code? Are there some foibles with the calendar on device I should be aware of, or ?