Google Calendar API email invitations delivery is inconsistent

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1

I’m working with Google Calendar API v3 to create calendar events and send invites to people, including external attendees. The problem is that email delivery is really unreliable. Some people always get the invitations, others never receive them, and some get them randomly.

Here’s my current code for creating events:

calendarService.events.insert({
    calendarId: targetCalendarId,
    resource: eventData,
    conferenceDataVersion: 1,
    sendUpdates: 'all'
}, function(error, response) {
    // handle response
});

I also tried the older approach with sendNotifications: true but still getting the same inconsistent behavior.

I checked other posts about this issue but most solutions seem outdated since the API structure has changed.

Has anyone experienced similar issues with Google Calendar API not reliably sending event invitation emails? What could be causing this inconsistency?

Edit: I think this might be related to email filtering or spam detection. After switching the sender email to a different organizational account (not a personal one), the delivery seems more reliable now.