diff --git a/pepdbagent/modules/project.py b/pepdbagent/modules/project.py
index fd50ec9..2b43f5f 100644
--- a/pepdbagent/modules/project.py
+++ b/pepdbagent/modules/project.py
@@ -670,6 +670,12 @@ def _update_samples(
             old_samples = session.scalars(select(Samples).where(Samples.project_id == project_id))
 
             old_samples_mapping: dict = {sample.guid: sample for sample in old_samples}
+
+            # old_child_parent_id needed because of the parent_guid is sometimes set to none in sqlalchemy mapping :( bug
+            old_child_parent_id: Dict[str, str] = {
+                child: mapping.parent_guid for child, mapping in old_samples_mapping.items()
+            }
+
             old_samples_ids_set: set = set(old_samples_mapping.keys())
             new_samples_ids_list: list = [
                 new_sample[PEPHUB_SAMPLE_ID_KEY]
@@ -751,6 +757,8 @@ def _update_samples(
                         old_samples_mapping[current_id].sample = sample_value
                         old_samples_mapping[current_id].sample_name = sample_value[sample_name_key]
 
+                    # !bug workaround: if project was deleted and sometimes old_samples_mapping[current_id].parent_guid
+                    # and it can cause an error in history. For this we have `old_child_parent_id` dict
                     if old_samples_mapping[current_id].parent_guid != parent_id:
                         if history_sa_model:
                             if current_history:
@@ -758,7 +766,7 @@ def _update_samples(
                             else:
                                 current_history = HistorySamples(
                                     guid=old_samples_mapping[current_id].guid,
-                                    parent_guid=old_samples_mapping[current_id].parent_guid,
+                                    parent_guid=old_child_parent_id[current_id],
                                     sample_json=old_samples_mapping[current_id].sample,
                                     change_type=UpdateTypes.UPDATE,
                                 )
diff --git a/tests/test_project_history.py b/tests/test_project_history.py
index 9399c39..d5e09fe 100644
--- a/tests/test_project_history.py
+++ b/tests/test_project_history.py
@@ -66,7 +66,7 @@ def test_get_add_history_all_project(self, namespace, name, sample_name):
             prj_init = agent.project.get(namespace, name, tag="default", raw=False)
             prj = agent.project.get(namespace, name, tag="default", with_id=True)
 
-            prj["_sample_dict"][0]["sample_name"] = "new_sample_name"
+            # prj["_sample_dict"][0]["sample_name"] = "new_sample_name"
 
             del prj["_sample_dict"][1]
             del prj["_sample_dict"][2]