Save current level unassigns all actors in level sequence

Why saving current level unassigns all actors in level sequence?! I used to fix the problem with selecting actor and replace or fix actor references. But this time I saved level and none of them can be reassigned. neither replacing nor fixing references seem to not work at all! Any idea? or solution to at least secure the assigned actors not to go unassigned in this case?!

typical they wont respond nor fix any real issues!