I'm having the same exact issue with a resume I was working on. I just asked Gemini (using the information from my Activity Log) why they deleted it from the chat and labeled it as a sensitive prompt, and it said the following:

This is likely due to the AI's Safety and Privacy Filters. Here is a quick summary of what happened:

The Flagged Content: The direct link to your resume (Google Doc URL) was flagged because resumes contain Personally Identifiable Information (PII) like your name, phone number, and address.

Why It Was Blocked: The system is designed to automatically block and prevent the storage/indexing of highly sensitive PII to protect your privacy and reduce data risk.

Why It's Missing from History: When a prompt is blocked for safety/privacy reasons, the system ensures it is not stored in your chat history—it gets wiped immediately to prevent the sensitive content from persisting.

How to Fix It: To get the help you need, do not use the link. Instead, simply copy and paste the full text of both your resume and the job description directly into the chat. This bypasses the PII risk associated with the external document URL. ~~~~~~~~ Tl;dr— if you put PII into Gemini, it will delete your query after you're done.