this has happened to me before. It just turned into a common key for me, check if it did that for you
It did the same thing for me. It becomes invisible in your inventory. So go to the space where it would have been and click the rare crate with that. It worked for me idk if it was just lag.
Its a bug there working on it protip it ALWAYS goes int the first slot if empty and vanishes if it isnt.
