Strange issue. Check out the 2 images below. One is fine but the other shows the strange billboard effect which happens within Unity when I press play - this only happens about 1/3 of the time, the other 2/3 when I press play the trees look fine.
I thought I just fixed it by turning off Automatic graphics switching in the Energy Saver Prefs. The trees looked fine for about 5 Plays but then it did it again … the strange billboard images seem to change, notice that the image below has a different billboard image to the initial post.
It seems to happen mid-game as well. I just pressed play and the billboards looked fine but then suddenly changed to the strange billboards while the game was running.