[210489] Duplicants stuck at nonsense

Let me tell a story:

#1: Duplicant keep standing on that rock, he can't go anywhere, even there is no obstacle blocking the way (you see my Pointer in the middle, it's red = can't reach)

#2: but they can go somewhere nearer...

#3: and after reach that point, he automatically find his way out of that place

This happened to me twice, the same as above, I had to make him go half way first.

Below is my save game, RIGHT AT the moment of the story above

Surface UpHead Cycle 61.sav