The issue there is caused by Async loading.
You could change the slot to synchronous task, but doing that would freeze the game (waiting for all actors to respawn) to mitigate the result you see, but doing that would still NOT avoid the property (ref) being read from slot before target actor exists… because your actors are dynamically spawned, so the plug-in cannot predict which property is going to be restored before the referenced actor was respawned.