A slight shift in gravity probably does happen, but so small we don't notice. The whole universe is in flux, in change, and what we think is everyday forever is not true. The North Pole and the South Pole have flipped in the past. It will happen again. What will it cause? I don't know. But it surely might effect gravity also.
Like universal chaos... because gravity keeps the planets in their proper (happy) orbit, among many other things...
