The equations of nature are supposed to exhibit locality in the sense that the action depends on fields and their derivatives. i.e. comparing the values of fields at local points.
But two points on a light cone have 4D distance of zero and hence they can also be said to be local. Indeed two points nearly on a light cone will have a 4D distance of nearly zero.
So these points are also 'local'.
But worse, in general relativity, the shape of the light cones depend on the equations of motion so we don't even know which points are 'local' to another point without first solving the equations of GR.
So how can we preserve the concept that equations must be 'local' if we don't know which points are local until after solving the equations? Is this a paradox?