I created an app and defined a custom timeline-event. Than I created some events for an existing contact and they appeared on the activity timeline of the contact as expected. A few days later these events where no longer visible at the same contact.
I tried to update the events via the API. I got no error but still not visible. I tried to create a new event for a new not existing email -> A contact has been automatically created, but the event is not visible in the activity timeline of this contact (in the activity filter all events are enabled). The timestamp I used is in milliseconds and even if I do not specify any timestamp it makes no difference.
The link to the last contact is:
Why are the events not visible in the activity timeline?