Mac OSX特有の問題かもしれない
Assets Broken on OSX [Resolved]
https://steamcommunity.com/app/255710/discussions/0/1290690926864576353/

2017年5月21日 2時26分
I would really like to know the solution to this. Most mac users have this problem right now.

2017年5月21日 4時24分
Solution:
Adobe Application Manager, Steam Overlay,
CleanMyMac 3 were causing some sought of conflict.
Forcing close those applications resolved the issue for me.

なんかのコンフリクト？