Still happens in 5.6 too.
So, you select two pcg actors, and change the PCGGraph, all except one become “invisible”. (not really invisible, just that they all stack in the location of one PCG)
This happens whenever you do anything to a PCG, be it editiing the source PCG, changing the graph etc.
Red one now stacks on the green ones location, for no good reason.
As you can see, the PCGs reference the wrong spline for some reason, until being moved and dropped again:
so, how do I fix or work around this?