Causality is always preserved. If A happens in the past light cone of B in one frame, then it happens in the past light cone of B in all frames. If, on the ot

Causality is always preserved. If A happens in the past light cone of B in one frame, then it happens in the past light cone of B in all frames. If, on the other hand, neither A nor B are in each other's past light cones, then there are reference frames where A or B happen 'first', but 'first' is in quotes, because this difference in time is really an artifact of a coordinate choice, and not physically meaningful. The best way to think about time relationships is that events (points in spacetime) have a partial order given by the relationship 'is in the past lightcone of'. Some pairs of points have this relationship one way or the other, and it's transitive. However some pairs of points don't have this relationship, and there's no meaningful way to compare them. Attempting to do so is inappropriately forcing a classical viewpoint onto a data model that doesn't support it.