Mobs doesn't suffocate on farmland/grass path, this was fixed in the latest Java Edition version.

Step to Reproduce:
1. Build a mob chamber and place down sticky piston with farmland/grass path in front. (like in the screenshot)
2. Put any two-block tall mob into the chamber.
3. Turn on the sticky piston.
-> Mobs doesn't suffocate inside grass path/farmland.