When a variable of type AssetID is set to an asset on another level, the reference to the second asset is lost after reloading the project if the second asset is renamed.
No - this behavior occurs in 4.13 as well
When the editor reopens, ActorBP1 has lost it's reference and is set to None. ActorBP2 still holds its reference to ActorBP1.
Reference is held after editor restart if the asset name has changed.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-39042 in the post.