So I just tested that PokéVision site... It said a Paras was on the corner near my house. I went there and there was rustling grass, but no Paras appeared. After 8 minutes, the site said it was gone, and then the rustling grass indeed disappeared.
This makes me assume the site is attuned to the grass, but the problem is that for me, the grass NEVER spawns Pokémon

Does the grass work for any of y'all? I assumed it was broken just like the 3-step tracking feature.