When events are tweeted using the Twitter Auto-Share feature, the event’s Featured Image is not included as a media object.
Currently, the event’s Featured Image *may* display in certain circumstances, but only as part of a website preview, generated from the URL included in the tweet.
Situations where this currently takes place seem to be relegated to desktop users of twitter’s website, while mobile users do not see this preview.
Ideally, the Featured Image associated with an event to be tweeted would be inserted as a media object, allowing the Featured Image to be visible to any/all users viewing the tweet, regardless of the device/platform being used.
Tweet including media object: https://twitter.com/WomensCalendar/status/943893975861096448
Tween not including media object: https://twitter.com/WomensCalendar/status/947988322990702592
Documentation for developers of twitter apps looking to associate images as media objects in tweets can be viewed here: https://developer.twitter.com/en/docs/media/upload-media/overview
Thanks so much for your consideration!