I'm running into an issue with the 1.12.2z build where the ground trap will not recognize player placed dirt turned grass or grass blocks as valid blocks to start working. I've tried in both survival and creative mode and have not been able to get it to work. it will take bait, but it never uses the bait to start doing its task.

I had similar problem, but placing ground traps with 2-block gaps between each other worked.