When placing down the 2x2 dark oak sapling clusters they will not grow in most places. Turning the tick speed up does not make them grow and only certain spots in the world. Even when there is nothing above them that could block growth they still do not grow.

When placing many side by side eventually one will grow, if that tree is then destroyed nearby trees are somehow updated and will grow as well.

May be an issue with 2x2 jungle trees as well.