Thanks Paul! We will try to find this event by the name, but maybe we are so much in luck, that you also got a save?

The first screen snapshot below shows an example of graphics disappearing.  I would give you a link to a save file, but when I exited the game, restarted the game, then loaded the save file, the graphics were back as shown in the second screen snapshot below.

I realize this is the type of bug that is very difficult to find, but I wanted to make sure you are aware of it.