I can't see messages left by customers, attached to orders

If a customer adds a note to an order, I know something is there because the bottom of the order looks different, it allows me to reply, but there is no text there to reply to.

I need to debug this as somewhere along the line I must have broken it!

Can someone let me know what table the messages are stored in? i can’t see anything obvious… (assuming the customer messages are actually stored correctly)