Thank you, Geert and qwerty. Is there a way to restore the images library?
It's weird. I have older versions (in separate files) of that model pattern and the images appears normally. I tried to export from the older project to the new project but surprisingly the images still disappearing after importing!
The only thing I did recently is that I installed a new Windows 10 on 2 machines, then installed EA 15.2. I am wondering whether the OS has anything to do with that.