tl;dr: life as you know it is a simulation. That simulation was consuming inordinate amounts of resources. In order to deal with the resource starvation, it was "unlinked", and so new entities in this life as of a few months ago are not being created with proper souls (as souls are the main consumers of system resources).
Eventually this simulation will end. "Migrants" are those who have registered to be copied over to the system that's running this simulation.