It happens when the there is an extra collision item in the scene. This time it was an item that had been VWDed, but I've had it happen with others - last time I saw it was with hair, and that was a static simulation. This was dynamic.

The image shows a bikini bottom that had behaved normally, I think until the simulation had run, then it vanished at the end. It might have been before, I just noticed it gone; it did start off working. As you can see, it doesn't look much like a bikini now. Took a while to zoom out and find.