diff --git a/libensemble/history.py b/libensemble/history.py
index 1a6e9c755..02a532bbe 100644
--- a/libensemble/history.py
+++ b/libensemble/history.py
@@ -123,7 +123,7 @@ def __init__(
         self.last_started = -1
         self.last_ended = -1
 
-    def update_history_f(self, D: dict, safe_mode: bool) -> None:
+    def update_history_f(self, D: dict, safe_mode: bool, kill_canceled_sims: bool = False) -> None:
         """
         Updates the history after points have been evaluated
         """
@@ -154,13 +154,14 @@ def update_history_f(self, D: dict, safe_mode: bool) -> None:
             self.H["sim_ended_time"][ind] = time.time()
             self.sim_ended_count += 1
 
-        for j in range(self.last_ended + 1, np.max(new_inds) + 1):
-            if self.H["sim_ended"][j]:
-                self.last_ended += 1
-            else:
-                break
+        if kill_canceled_sims:
+            for j in range(self.last_ended + 1, np.max(new_inds) + 1):
+                if self.H["sim_ended"][j]:
+                    self.last_ended += 1
+                else:
+                    break
 
-    def update_history_x_out(self, q_inds: npt.NDArray, sim_worker: int) -> None:
+    def update_history_x_out(self, q_inds: npt.NDArray, sim_worker: int, kill_canceled_sims: bool = False) -> None:
         """
         Updates the history (in place) when new points have been given out to be evaluated
 
@@ -180,7 +181,8 @@ def update_history_x_out(self, q_inds: npt.NDArray, sim_worker: int) -> None:
         self.H["sim_worker"][q_inds] = sim_worker
 
         self.sim_started_count += len(q_inds)
-        self.last_started = np.max(q_inds)
+        if kill_canceled_sims:
+            self.last_started = np.max(q_inds)
 
     def update_history_to_gen(self, q_inds: npt.NDArray):
         """Updates the history (in place) when points are given back to the gen"""
diff --git a/libensemble/manager.py b/libensemble/manager.py
index 426b54738..9df20935e 100644
--- a/libensemble/manager.py
+++ b/libensemble/manager.py
@@ -377,7 +377,7 @@ def _update_state_on_alloc(self, Work: dict, w: int):
 
         work_rows = Work["libE_info"]["H_rows"]
         if Work["tag"] == EVAL_SIM_TAG:
-            self.hist.update_history_x_out(work_rows, w)
+            self.hist.update_history_x_out(work_rows, w, self.kill_canceled_sims)
         elif Work["tag"] == EVAL_GEN_TAG:
             self.hist.update_history_to_gen(work_rows)
 
@@ -403,6 +403,7 @@ def _receive_from_workers(self, persis_info: dict) -> dict:
         communticate. If any output is received, all other workers are
         looped back over.
         """
+        time.sleep(0.0001)  # Critical for multiprocessing performance
         new_stuff = True
         while new_stuff:
             new_stuff = False
@@ -433,7 +434,7 @@ def _update_state_on_worker_msg(self, persis_info: dict, D_recv: dict, w: int) -
                 if calc_status is FINISHED_PERSISTENT_GEN_TAG and self.libE_specs.get("use_persis_return_gen", False):
                     self.hist.update_history_x_in(w, final_data, self.safe_mode, self.W[w - 1]["gen_started_time"])
                 elif calc_status is FINISHED_PERSISTENT_SIM_TAG and self.libE_specs.get("use_persis_return_sim", False):
-                    self.hist.update_history_f(D_recv, self.safe_mode)
+                    self.hist.update_history_f(D_recv, self.safe_mode, self.kill_canceled_sims)
                 else:
                     logger.info(_PERSIS_RETURN_WARNING)
             self.W[w - 1]["persis_state"] = 0
@@ -446,7 +447,7 @@ def _update_state_on_worker_msg(self, persis_info: dict, D_recv: dict, w: int) -
             self._freeup_resources(w)
         else:
             if calc_type == EVAL_SIM_TAG:
-                self.hist.update_history_f(D_recv, self.safe_mode)
+                self.hist.update_history_f(D_recv, self.safe_mode, self.kill_canceled_sims)
             if calc_type == EVAL_GEN_TAG:
                 self.hist.update_history_x_in(w, D_recv["calc_out"], self.safe_mode, self.W[w - 1]["gen_started_time"])
                 assert (
@@ -485,8 +486,10 @@ def _handle_msg_from_worker(self, persis_info: dict, w: int) -> None:
 
     def _kill_cancelled_sims(self) -> None:
         """Send kill signals to any sims marked as cancel_requested"""
+
         if self.kill_canceled_sims:
             inds_to_check = np.arange(self.hist.last_ended + 1, self.hist.last_started + 1)
+
             kill_sim = (
                 self.hist.H["sim_started"][inds_to_check]
                 & self.hist.H["cancel_requested"][inds_to_check]