open ai llm model not responding using faiss db for few iteration in the start of a conversation

Question

I am trying to build a pdf search and chatbot engine. In the beginning of my conversation if i ask my model to provide me pdf published in year 2020 it is not responding, but asking the same question 3 4 times it start responding. What could be the issue. Db - Faiss, llm model - openai, langchain - conversationretreivelchain function i am using, for extracting meta data and adding it with pdf to get chunk i am using pypdf2

i have pdf published in 2020 in my db