A month or two ago I was digging out a large mountain and I didn't want to wait for all the dirt blocks to update to grass blocks. To remedy this, I of course increased my random tick speed. To my avail, setting my random tick speed to something higher than one caused everything that relied on a random tick speed to stop working. I've had this issue since v1.8 and I figured it would have been reported by now. This issue fixes itself whenever you create a new world, but I don't want to create a new world every time I want to grow crops.