diff --git a/rdagent/utils/workflow/loop.py b/rdagent/utils/workflow/loop.py
index 9fdaa529..34dc119e 100644
--- a/rdagent/utils/workflow/loop.py
+++ b/rdagent/utils/workflow/loop.py
@@ -10,6 +10,7 @@ Postscripts:
 
 import asyncio
 import concurrent.futures
+import copy
 import os
 import pickle
 from collections import defaultdict
@@ -227,7 +228,11 @@ class LoopBase:
                     if force_subproc:
                         curr_loop = asyncio.get_running_loop()
                         with concurrent.futures.ProcessPoolExecutor() as pool:
-                            result = await curr_loop.run_in_executor(pool, func, self.loop_prev_out[li])
+                            # Using deepcopy is to avoid triggering errors like "RuntimeError: dictionary changed size during iteration"
+                            # GUESS: Some content in self.loop_prev_out[li] may be in the middle of being changed.
+                            result = await curr_loop.run_in_executor(
+                                pool, copy.deepcopy(func), copy.deepcopy(self.loop_prev_out[li])
+                            )
                     else:
                         # auto determine whether to run async or sync
                         if asyncio.iscoroutinefunction(func):