The disappearance of a randomly selected 50% of the population would be a catastrophe on a gigantic scale.
Then having that 50% suddenly reappear, unaware that any time has passed, and presumably believing they own houses and other things that have since been claimed/redistributed, AND there's a sudden need to again feed four billion more people. Like, can you imagine the run on the grocery store when your town's population doubles on size instantaneously?