I have a similar problem with Riverview, especially when I first start a game there. All action will stop every 10-20 minutes (real time), except for the animation on the plumbob, the "zzzzz" from sleeping, butterflies, etc. Then, after a few sim weeks of playing that file, it simply goes away. The only thing I can figure is that something going on somewhere in the town is dragging the game down and after a while, whatever it is that's doing it suddenly stops happening.