I have been experiencing this disappearing city problem since I started the game Darkstar. Not sure how long that has been....4 months? It is what happens right before shockwave flash crashes. The way the crash would happen is this: I would visit the first city, and all was fine, by the third or fourth city half of the buildings would disappear. If I loaded another city after that it would be all black. If I managed to catch the issue before the cities turn black, just refreshing would fix it. If however, the cities turned black, the only way to fix was to close all the windows in the browser, shut down the browser (chrome) and reopen the browser and then reopen all my browser windows.
Since the hardware acceleration, I have a lot fewer crashes. I have other issues, but the crashes are much better. Now I only crash once or twice giving all the neighborly help. It is a lot longer to load a city from the world map, but the crashes are few and far between.