Hi! Yes, I had reports that this auto-spawned camera system actor was causing problems with level streaming, and in fact was causing a few other problems elsewhere too, such as OwnerSee/NoSee flags on components, Sequencer cameras, and more.
In the upcoming 5.6 I’ve just abandoned the auto-spawned camera system actor, as it turned out to be a bad idea… apologies about this.
In the meantime, you can indeed either use that CVar to fix the issue, or patch the camera system actor with some code to move its transform where the evaluated camera was last computed (from its camera system component).