Training RAG but getting "###" as a answer

Question

I'm currently training a Rag chatbot with PDF using Mistral AI it use to work but since 1 day i only get "###########################" as an answer and i don't know why !

query_engine = index.as_query_engine()
response = query_engine.query("hello?")

print(response)

output : ################################################################################################################################################################################################################################################################

here is a link to the google colab : https://colab.research.google.com/drive/1Qt68-7Q9NAug4HLkX5MEICkjHT5-r-q-

I would love some help if you guys know what's going on !