This is similar to MCPE-12954, but applies to Grass Paths, and not pure Grass blocks. The bug is that when placing fences or fence gates (or Hoppers) on Grass Paths the block turns into Dirt (and after a while into a plain Grass block again).

(In MCPE-12954 you are also able to place beds on Grass, but now you're not able to place beds on Grass Paths at all, but I guess that could be considered to be "as intended", so I'm just mentioning it here as a side note.)

I've attached two images, one with some fences on Grass with the Grass Path next to them, and one after placing the fences and Hopper.