See the attached screenshot. Previously in 19w40a, as well as every single previous version of minecraft i have played back to at least 1.8, in this layout al 18 saplings in the picture would grow. currenly only the 4 in the middle have grown. they all meet the requirements to grow, they just have stopped in this pre release. The chunks were loaded for 24 hours straight, and bonemealed with 6 stacks of bonemeal and they refuse to grow.