diff --git a/platypush/entities/_engine/repo/db.py b/platypush/entities/_engine/repo/db.py
index 77a5668c9d..1114da34b2 100644
--- a/platypush/entities/_engine/repo/db.py
+++ b/platypush/entities/_engine/repo/db.py
@@ -83,8 +83,8 @@ class EntitiesDb:
         already been flushed.
         """
         # Index childrens by parent_id and by parent_key
-        children_by_parent_id = defaultdict(list)
-        children_by_parent_key = defaultdict(list)
+        children_by_parent_id = defaultdict(lambda: defaultdict(Entity))
+        children_by_parent_key = defaultdict(lambda: defaultdict(Entity))
         for entity in entities:
             parent_key = None
             parent_id = entity.parent_id
@@ -93,9 +93,9 @@ class EntitiesDb:
                 parent_key = entity.parent.entity_key
 
             if parent_id:
-                children_by_parent_id[parent_id].append(entity)
+                children_by_parent_id[parent_id][entity.entity_key] = entity
             if parent_key:
-                children_by_parent_key[parent_key].append(entity)
+                children_by_parent_key[parent_key][entity.entity_key] = entity
 
         # Find the root entities in the hierarchy (i.e. those that have a null
         # parent)
@@ -131,14 +131,17 @@ class EntitiesDb:
             # Index the children nodes by key
             children_to_process = {
                 e.entity_key: e
-                for e in children_by_parent_key.get(entity.entity_key, [])
+                for e in children_by_parent_key.get(entity.entity_key, {}).values()
             }
 
             # If this entity has already been persisted, add back its children
             # that haven't been updated, so we won't lose those connections
             if entity.id:
                 children_to_process.update(
-                    {e.entity_key: e for e in children_by_parent_id.get(entity.id, [])}
+                    {
+                        e.entity_key: e
+                        for e in children_by_parent_id.get(entity.id, {}).values()
+                    }
                 )
 
             # Add all the updated+inserted+existing children to the next layer
diff --git a/platypush/entities/_engine/repo/merger.py b/platypush/entities/_engine/repo/merger.py
index cb397c2684..b3b88dd45b 100644
--- a/platypush/entities/_engine/repo/merger.py
+++ b/platypush/entities/_engine/repo/merger.py
@@ -51,6 +51,19 @@ class EntitiesMerger:
         processed_entities = []
         existing_entities.update(self._repo.get(session, entities, use_cache=False))
 
+        # Make sure that we have no duplicate entity keys in the current batch
+        entities = list(
+            {
+                **({e.entity_key: e for e in entities}),
+                **(
+                    {
+                        e.entity_key: e
+                        for e in {str(ee.id): ee for ee in entities if ee.id}.values()
+                    }
+                ),
+            }.values()
+        )
+
         # Retrieve existing records and merge them
         for entity in entities:
             key = entity.entity_key
@@ -109,6 +122,7 @@ class EntitiesMerger:
             else:
                 temp_entity = new_entities.get(parent.entity_key)
                 if temp_entity:
+                    self._remove_duplicate_children(entity, temp_entity)
                     parent = entity.parent = temp_entity
                 else:
                     new_entities[parent.entity_key] = parent
@@ -125,6 +139,34 @@ class EntitiesMerger:
 
         return parent_id, parent
 
+    @staticmethod
+    def _remove_duplicate_children(entity: Entity, parent: Optional[Entity] = None):
+        if not parent:
+            return
+
+        # Make sure that an entity has no duplicate entity IDs among its
+        # children
+        existing_child_index_by_id = None
+        if entity.id:
+            try:
+                existing_child_index_by_id = [e.id for e in parent.children].index(
+                    entity.id
+                )
+                parent.children.pop(existing_child_index_by_id)
+            except ValueError:
+                pass
+
+        # Make sure that an entity has no duplicate entity keys among its
+        # children
+        existing_child_index_by_key = None
+        try:
+            existing_child_index_by_key = [e.entity_key for e in parent.children].index(
+                entity.entity_key
+            )
+            parent.children.pop(existing_child_index_by_key)
+        except ValueError:
+            pass
+
     @classmethod
     def _merge_columns(cls, entity: Entity, existing_entity: Entity) -> Entity:
         """
diff --git a/platypush/plugins/zigbee/mqtt/__init__.py b/platypush/plugins/zigbee/mqtt/__init__.py
index a857962eed..46ec198774 100644
--- a/platypush/plugins/zigbee/mqtt/__init__.py
+++ b/platypush/plugins/zigbee/mqtt/__init__.py
@@ -904,7 +904,7 @@ class ZigbeeMqttPlugin(MqttPlugin):  # lgtm [py/missing-call-to-init]
                 workers[device].join(timeout=kwargs.get('timeout'))
             except Exception as e:
                 self.logger.warning(
-                    'An error while getting the status of the device {}: {}'.format(
+                    'An error occurred while getting the status of the device {}: {}'.format(
                         device, str(e)
                     )
                 )