Thank you so much for your response @Alberto_Umana !

The changes you mentioned about retriever worked and I don't have error with retriever anymore.

But I am still facing issues with llm_endpoint and the error is: 

MlflowException: Failed to save runnable sequence: {'2': "ChatDatabricks -- No module named 'langchain_databricks'"}.

My code is now exactly the same as you have mentioned in the post. 

thank you!