In version 1.2.0 of the better together release on Xbox One:
I have a lot of dirt around my house surrounded by grass as well as a sheep farm. I have not seen a single block of dirt grow grass in the past 12 in-game days. None of my sheep are regrowing their wool because the pen has no grass in it. All this grass has direct access to the sky, and has torches nearby.

Either the grass is growing so slow that it might as well not grow at all, or it just isn't growing at all. Fix it by making it grow at the rate it used to in older versions.