One answer should be that if it is isolated and keep expand forever, the overall entropy does increase nonstop.
But if the universe can reach a point in spacetime when it starts collapsing instead of expanding you could argue that the energy which has been spread out over vast distancies (cold objects, CMB) will now be doing work in this crunch and if the crunch results in a new universe (big bang) obviously at some time it must go against the second law and decrease.
I´m not sure how to decide when the internal entropy starts to decrease. But if the crunch actually spawns a new universe surely it must be a large drop in entropy during a big bang? A thought is that entropy doesn't really change on the universal scale, only locally.