From 8/17/16 Tools sync: This is probably also happening in Sequencer. Think Sequencer should just auto-set this flag.
If a SkeletalMesh actor is placed beyond view of the player, and a Matinee (which does NOT play on level load) triggers an animation sequence (the animation moves the bones into the area near the player), then the mesh is not updated and not visible to the player.
1. Load QA Game
2. If you are on the default map with the small floor, scale the floor up so it covers a much wider area.
3. Import a SkeletalMesh and an Animation where the rig is translated over a large distance (FBX files attached)
4. Place the SkeletalMesh into the level, then set it around -30 Z Location, so that it is below the map.
5. Make a Matinee. Add the SkeletalMesh to a SkeletalMesh Group. Set it to play its animation in the Animation Track. (make sure, while in the Matinee, that the updated position of the mesh is above the floor)
6. In the Level Blueprint, set up a Event Play > Delay 2 seconds > Play Matinee.
7. Play in Editor
RESULT: If your floor is wide enough to block sight to the starting position of the mesh, then after 2 seconds, nothing happens and the mesh does not appear above the floor.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-8191 in the post.