diff --git a/main/lib/idds/core/health.py b/main/lib/idds/core/health.py
index 074f0e62..90777379 100644
--- a/main/lib/idds/core/health.py
+++ b/main/lib/idds/core/health.py
@@ -96,6 +96,6 @@ def select_agent(name, newer_than=3600, session=None):
         if selected_agent['status'] != HealthStatus.Active:
             orm_health.update_health_item_status(selected_agent, status=HealthStatus.Active, session=session)
     for health_item in health_items:
-        if health_item['status'] == HealthStatus.Active and health_item != selected_agent:
+        if health_item['agent'] == name and health_item['status'] == HealthStatus.Active and health_item['health_id'] != selected_agent['health_id']:
             orm_health.update_health_item_status(selected_agent, status=HealthStatus.Default, session=session)
     return selected_agent
diff --git a/main/lib/idds/orm/base/alembic/versions/6ca0e5e466eb_update_message_null_constraints.py b/main/lib/idds/orm/base/alembic/versions/6ca0e5e466eb_update_message_null_constraints.py
index b477aa3e..45272c82 100644
--- a/main/lib/idds/orm/base/alembic/versions/6ca0e5e466eb_update_message_null_constraints.py
+++ b/main/lib/idds/orm/base/alembic/versions/6ca0e5e466eb_update_message_null_constraints.py
@@ -17,7 +17,6 @@
 """
 from alembic import op
 from alembic import context
-import sqlalchemy as sa
 
 
 # revision identifiers, used by Alembic.
@@ -30,14 +29,15 @@
 def upgrade() -> None:
     if context.get_context().dialect.name in ['oracle', 'mysql', 'postgresql']:
         schema = context.get_context().version_table_schema if context.get_context().version_table_schema else ''
-        op.alter_column('messages', sa.Column('request_id'), nullable=True, schema=schema)
-        op.alter_column('messages', sa.Column('transform_id'), nullable=True, schema=schema)
-        op.alter_column('messages', sa.Column('processing_id'), nullable=True, schema=schema)
+        op.alter_column('messages', 'request_id', nullable=True, schema=schema)
+        op.alter_column('messages', 'transform_id', nullable=True, schema=schema)
+        op.alter_column('messages', 'processing_id', nullable=True, schema=schema)
 
 
 def downgrade() -> None:
     if context.get_context().dialect.name in ['oracle', 'mysql', 'postgresql']:
         schema = context.get_context().version_table_schema if context.get_context().version_table_schema else ''
-        op.alter_column('messages', sa.Column('request_id'), nullable=False, schema=schema)
-        op.alter_column('messages', sa.Column('transform_id'), nullable=False, schema=schema)
-        op.alter_column('messages', sa.Column('processing_id'), nullable=False, schema=schema)
+        # here doesn't update nullable to False, since the table may have null rows which will cause failure.
+        op.alter_column('messages', 'request_id', nullable=True, schema=schema)
+        op.alter_column('messages', 'transform_id', nullable=True, schema=schema)
+        op.alter_column('messages', 'processing_id', nullable=True, schema=schema)