As far as I understand it, I'd think it'd have a lot to do with the orbits of the planets relative to each other. Particularly with the largest planets, Jupiter and Saturn. Jupiter has an orbital period of (checks numbers) about 12 Earth years, whereas Saturn's orbit takes closer to 30 years. As the planets orbit, their combined gravitational fields will mean that the lagrange points will move quite considerably over time, and may well amplify/interfere with each other and those of the other planets at certain times. So a node may "shift" between different sets of these points, or may disappear entirely, be it for a few seconds or a few centuries depending on the planets' positions relative to each other and the star. Any system with particularly massive planets will suffer this more often, and systems with few or no massive planets will have very stable nodes. But if and when one of these nodes collapses, it may not reappear for a very long time, until the gravitational forces have made conditions favourable again.