Attaching / Detaching a blueprint actor to a player in a network environment causes location errors when the detach occurs. Even without the attach events being replicated or the blueprint's movement being replicated (replicating movement stops this from occurring), the cube is moved on the client. When the detach occurs, the cube resets to 0,0,0 instead of staying at its location or even resetting to its original location.
Another odd thing, although this may just be a symptom of doing networking tests in PIE, if you eject (F8) on Player 1 (the server), the cube also goes to 0,0,0. Whether you eject or not, after the detach, the blueprint also shows as being at 0,0,0 in the World Outliner, although it is not on the Server if an eject hasn't occurred.
Link to project: [Link Removed]
This also occurred in 4.13/4.14
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