As you say, event order is not preserved: two events that appear simultaneous to one observer can easily appear in different orders to other observers. But cau

As you say, event order is not preserved: two events that appear simultaneous to one observer can easily appear in different orders to other observers. But causality itself is safe in relativity: if a signal from event A could possibly reach event B (given the speed of light limit), then every reference frame will agree that A comes before B. The only events whose relative order is indeterminate are those separated by enough distance (relative to elapsed time that one couldn't influence the other: events who are not in each other's "light cones".