be safe and check the error relative to the stored old dx_max_sort.

src/runner_doiact.h

@@ -918,7 +918,7 @@ void DOPAIR1(struct runner *r, struct cell *ci, struct cell *cj, const int sid,
                     p->x[1] * runner_shift[sid][1] +
                     p->x[2] * runner_shift[sid][2];
     if (fabsf(d - sort_i[pid].d) - ci->dx_max_sort >
-        1.0e-6 * max(fabsf(d), ci->dx_max_sort))
+        1.0e-6 * max(fabsf(d), ci->dx_max_sort_old))
       error(
           "particle shift diff exceeds dx_max_sort in cell ci. ci->nodeID=%d "
           "cj->nodeID=%d d=%e sort_i[pid].d=%e ci->dx_max_sort=%e "
@@ -932,7 +932,7 @@ void DOPAIR1(struct runner *r, struct cell *ci, struct cell *cj, const int sid,
                     p->x[1] * runner_shift[sid][1] +
                     p->x[2] * runner_shift[sid][2];
     if (fabsf(d - sort_j[pjd].d) - cj->dx_max_sort >
-        1.0e-6 * max(fabsf(d), cj->dx_max_sort))
+        1.0e-6 * max(fabsf(d), cj->dx_max_sort_old))
       error(
           "particle shift diff exceeds dx_max_sort in cell cj. cj->nodeID=%d "
           "ci->nodeID=%d d=%e sort_j[pjd].d=%e cj->dx_max_sort=%e "