A sequence created in UMG appears to skip/ignore the first frame. If an event is set to fire off on the first frame of the sequence it will not fire.
Result: The event on the first frame of the sequence animation in the widget does not fire
Expected: The event on the first frame would fire off for the widget (a print string will fire in this test case)
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-76352 in the post.