eko :
It's OK, I will put some invi pillars in there :3

Hi Yeehan, for some reason the game won't let me update the model.
Unfortunately faces of these pillars are flipped. Unreal Engine handles this so the ball can pass through backside (NoCollision) and gets blocked on the frontside (Collision).
In this very rare case i suggest:
Place another object (obstacle) around these pillars to prevent getting blocked.

I apologize but i do not want to delete this asset and upload a new version. Hope it helps.

Dear eko :
I got stuck in the pillar of the wooden stair

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1552458823
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1552459265

and seems like all the pillar will stuck the ball :'(