One of the things I like most about my customer-facing technical role is that users find the craziest bugs. My favorite is a bug in a chat program that would keep channels from rendering and crash the client. The only clue I got was "it seems to be affecting channels used by HR more than other departments, but it's spreading."
Turns out the rendering engine couldn't handle a post that was an emoji followed by a newline and then another emoji. So when the HR team posted this, meaning "hair on fire" it broke things: