When I walk on terrain with a Character Controller my memory usage consistently goes up.
I tested this by using the Terrain map in the MyGame project with a Character Controller using the FPSplayer.script. I also put a check for memory usage and collectgarbage() in my main App Loop.
Further details can be found in the video I made--
https://www.youtube.com/watch?v=Bj0brR8_7eQ&feature=youtu.be