This conjecture has become a dogma since 1905 and it is simply not true.
There exists a class of events which have definite absolute temporal relation
of succession.
Given a motion of a line segment AB passing a point P, A first then B:
There is no inertial system in which the kinematic event of A passing P and B passing P could be "seen" it in a different order
Einstein's statement:
There is no absolute (independent of the space of reference) relation in space, and no absolute relation in time between two events, but there is an absolute (independent of the space of reference) relation in space and time,
If the point P is between A and B there is no coordinate system in space where it would be outside of A B .
Whatever that statement means it unnecessary disregards simple tempora and spatial reasoning valid without invoking the spacetime cluster.