This seems like a bug, not a feature. What is the point of a project if chats cannot read one another?
Projects can use context from other chats in the same project, subject to memory and workspace settings: https://help.openai.com/en/articles/10169521. That doesn't guarantee verbatim recall of every message. If it's still failing, please share the exact non-sensitive example and whether project/account memory is enabled so Support can check the behavior.