diff --git a/autogpt_platform/backend/backend/data/graph.py b/autogpt_platform/backend/backend/data/graph.py
index 759a303c4b..3340716da8 100644
--- a/autogpt_platform/backend/backend/data/graph.py
+++ b/autogpt_platform/backend/backend/data/graph.py
@@ -683,7 +683,7 @@ class GraphModel(Graph, GraphMeta):
                 continue
             for key, value in node.input_default.items():
                 if isinstance(value, dict) and "_credentials_id" in value:
-                    value["_credentials_id"] = None
+                    del value["_credentials_id"]
 
     def validate_graph(
         self,
diff --git a/autogpt_platform/backend/backend/data/graph_test.py b/autogpt_platform/backend/backend/data/graph_test.py
index 066cd3a3de..ff49db531e 100644
--- a/autogpt_platform/backend/backend/data/graph_test.py
+++ b/autogpt_platform/backend/backend/data/graph_test.py
@@ -560,8 +560,9 @@ def test_reassign_ids_clears_credentials_id():
 
     GraphModel._reassign_ids(graph, user_id="new-user", graph_id_map={})
 
-    # _credentials_id should be cleared
-    assert graph.nodes[0].input_default["spreadsheet"]["_credentials_id"] is None
+    # _credentials_id key should be removed (not set to None) so that
+    # _acquire_auto_credentials correctly errors instead of treating it as chained data
+    assert "_credentials_id" not in graph.nodes[0].input_default["spreadsheet"]
 
 
 def test_reassign_ids_preserves_non_credential_fields():
@@ -668,8 +669,8 @@ def test_reassign_ids_handles_multiple_credential_fields():
 
     GraphModel._reassign_ids(graph, user_id="new-user", graph_id_map={})
 
-    assert graph.nodes[0].input_default["spreadsheet"]["_credentials_id"] is None
-    assert graph.nodes[0].input_default["doc_file"]["_credentials_id"] is None
+    assert "_credentials_id" not in graph.nodes[0].input_default["spreadsheet"]
+    assert "_credentials_id" not in graph.nodes[0].input_default["doc_file"]
     assert graph.nodes[0].input_default["plain_input"] == "not a dict"
 
 
diff --git a/autogpt_platform/backend/backend/executor/utils.py b/autogpt_platform/backend/backend/executor/utils.py
index e3d24be556..ffccd125b9 100644
--- a/autogpt_platform/backend/backend/executor/utils.py
+++ b/autogpt_platform/backend/backend/executor/utils.py
@@ -353,6 +353,15 @@ async def _validate_node_input_credentials(
                     )
 
                 if field_value and isinstance(field_value, dict):
+                    if "_credentials_id" not in field_value:
+                        # Key removed (e.g., on fork) — needs re-auth
+                        has_missing_credentials = True
+                        credential_errors[node.id][field_name] = (
+                            "Authentication missing for the selected file. "
+                            "Please re-select the file to authenticate with "
+                            "your own account."
+                        )
+                        continue
                     cred_id = field_value.get("_credentials_id")
                     if cred_id and isinstance(cred_id, str):
                         try:
@@ -367,9 +376,9 @@ async def _validate_node_input_credentials(
                         if not creds:
                             has_missing_credentials = True
                             credential_errors[node.id][field_name] = (
-                                "The saved Google credentials are not available "
+                                "The saved credentials are not available "
                                 "for your account. Please re-select the file to "
-                                "authenticate with your own Google account."
+                                "authenticate with your own account."
                             )
 
         # If node has optional credentials and any are missing, mark for skipping