Allow me to make a wild guess, all in the mind of: Could it be the case that .....
So ... could it be that you started with solid rocks and the pathfinder on default obstacles: solid. Then you changed to custom obstacles. Added them in the 'on start of layout', and it worked.
Well somewhere (on a dark place where i can not bring my dull brain) there is a obstacle map. And there is only one. Meaning, it is not private/instance or object. This map is catched, for performance. So when you (in the could it be that case still) changed to custom obstacles, this map was still catched by the browser. But that did not rest that long.
Your current (the one shown above) events can not work at all. Because you forgot to use the action sprite > pathfinding > Regenerate obstacle map directly after adding the obstacles.
Dont forget: if you move a rock. You should use 'Regenerate region around object'. And find new paths.