MS 365 Copilot Notebooks Does Not Honor Instructions

I have uploaded 3 reference spreadsheets to a Copilot notebook. They contain data dictionary and metadata of a SQL database. In my Copilot Instructions (currently 1,652 characters) I specify that I want Copilot to ask me clarifying questions if anything in the question is unclear. Additionally, my Copilot Instructions include the ask to use provided reference files to find appropriate field names instead of conjuring them out of thin air.

Unfortunately, In many of the answers Copilot ignores those guardrails and provides fake field names when asked to create a SQL query. 

Why is that and how can I improve accuracy of Copilot's answers?